same plot, the lowest percentage of dry matter was only 107, and the highest 197, the ratio being 100: 184. In three other varieties the ratios came out 100: 183; 100: 184; 100: 179. The sugar and nitrogen vary still more widely. In 100 individual roots of one variety, grown side by side on the same plot, the following were the limits: Throughout the examination of the individual roots careful records have been kept of the shape, size and colour of each root which has been sampled and examined. Shape and colour do not appear to be in any way correlated with any peculiarity of chemical composition. As regards size, a mixed sample from fifty large roots is certain to contain a lower percentage of dry matter and sugar than a mixed sample from fifty small roots of the same variety grown under identical conditions, but there is nothing like inverse proportionality between size of root and percentage of dry matter. Among the 1,000 roots examined many large ones have been found containing high percentages of dry matter, and vice versa. By saving such large roots with high percentages of dry matter for seed-mothers it should be possible to improve the race. Again, there appears to be no definite correlation between percentages of dry matter, sugar, and proteid and non-proteid nitrogen. Each appears to vary independently of the rest. It should therefore be possible, by continuously selecting as seed-mothers roots of definite composition, to change the composition of the race in any desired direction. Experiments of this kind are already in progress on the University Farm. MONDAY, AUGUST 22. The following Papers were read:- 1. On the Forms of Stems of Plants. By LORD AVEBURY, D.C.L., F.R.S. Some plants have round stems, some square, some triangular, some pentagonal. No doubt there are reasons for these and other forms, but the author found no explanation in botanical works. It is, of course, important for plants, as for architects, to obtain the greatest strength with the least expenditure of material. To do this it is necessary that the plant should be equally liable to rupture at every point when the strain is equal. If not, it is obvious that a certain amount of material may be removed from the strongest part without increasing the danger of rupture. If the stem of a plant, or any other pillar, is affected by pressure-say of wind-one side will be extended and the other compressed, while between them will be a neutral axis, and both extension and compression will be greatest along the surface farthest from the neutral axis. It follows, therefore, that the strongest form is where the material is collected as far as possible from the neutral axis. The two bars cannot, however, be entirely separate, and must therefore be connected by a bar or bars. This is the origin of the well-known girder (fig. 1). If the forces to be resisted act in two directions at right angles to one another, two girders must be combined, one at right angles to the other. If the forces act in all directions, a circular series of girders will be required, as Schwendener and others have pointed out. This is the case in the stems of trees, where the woody fibres form a ring, only separated in places by what are known as the medullary' rays. This is the reason for the prevalent round form of stems. The question then arises, Why is this form not universal? As regards plants having quadrangular stems, it may be pointed out that when the leaves were in opposite pairs, each pair at right angles to those above and below, as, for instance, in the dead nettle, the strain of the wind would be mainly in two directions, and the 'double girder' (fig. 2) would be the best form. If so we should expect to find quadrangular stems associated with opposite leaves. The author then took the British flora, and showed that plants with quadrangular stems always have opposite leaves, and that plants with opposite leaves have generally, though with exceptions, quadrangular stems. The reasons for these exceptions were then considered. Passing to triangular stems, it was pointed out that they might be accounted for by the same considerations. Many Monocotyledons, but not all, have the leaves in threes. Sedges, for instance, all have more or less triangular stems, while in FIG. 1. FIG. 2. H grasses they are round. Now, sedges have leaves in threes, while in grasses they are distichous, i.e. in two rows or ranks. In plants with pentagonal stems the same relation prevails. The bramble, for instance, has a stem more or less pentagonal, and the leaves are in whorls of fives, a character, as he incidentally observed, which throws light on the number of petals and sepals. The petals represent a whorl of leaves, and as a rule, when the whorl consists of five leaves, the flower has five petals and five sepals; while when the leaves are opposite a whorl would consist of four leaves, as, for instance, in veronica, where also there are four petals. Thus, then, the author finally remarked, plants have worked out for themselves, millions of years ago, principles of construction so as to secure the greatest strength with the least expenditure of materials, which have been gradually applied to the construction of buildings by the skill and science of our architects and engineers. 2. On Recent Researches on Parasitic Fungi. 3. On the Vegetative Life of some Uridineæ. 4. On the Development of the Ecidium of Uromyces Pox, and on the LifeHistory of Puccinia Malvacearum. By V. H. BLACKMAN and Miss HELEN C. I. FRASER. TUESDAY, AUGUST 23. The following Papers were read : 1. Sunshine and CO2-Assimilation: an Account of Experimental Researches. By Dr. F. F. BLACKMAN and Miss MATTHAEI. 2. Struggle for Pre-eminence and Inhibitory Stimuli in Plants. By Professor L. ERRERA. Vegetable physiology, like animal physiology, presents a great number of cases of suspensory stimuli, or inhibitory phenomena: arrest of growth of the fructiferous filament of Phycomyces during the formation of the sporangium; influence of wounds on the growth, and irritability of certain organs (traumatic shock); retarding effect of light on elongation, &c. It is also in this way that the influence exercised by the apex of many plants on the subjacent ramifications with which it finds itself in some way struggling for pre-eminence can best be understood. The apex of Picea excelsa, for instance, hinders the side-branches from rising geotropically. If one suppresses it, or if it is notably weakened, a conflict for supremacy obtains between the branches themselves; generally one of the branches nearest the summit, or the strongest among equidistant ones, prevails and forms a new summit. The apex continues to make itself felt even after the removal of a ring of bark; its action then probably proceeds through the living cells of the pith and the medullary rays. On the other hand, in the Araucarias (where the regeneration of the summit is effected by new buds, and not by the rising of already developed branches) the action of the apex is conducted by the bark, and an annular incision is equivalent to cutting off the top. Several arguments can be quoted to support the existence of inhibitory stimuli emanating from the apex, and the production of 'suckers' (gourmands) and of 'witches' brooms' can be connected with it. 3. On the Proteases of Plants. By Professor S. H. VINES, F.R.S. 6 As the result of observations made in the course of the last three years, of which accounts have been published from time to time in the Anuals of Botany,' I have demonstrated the very general occurrence of proteases in all parts of plants. With regard to the nature of the proteases, it has been ascertained, in the first place by means of the tryptophane-reaction, that their action is peptolytic-that is, that they decoinpose peptones and albumoses into non-proteid substances such as leucin, tyrosin, and other amido-acids. In no case was peptonisation observed without peptolysis; whence it follows that the proteases are not of the nature of pepsin, but rather correspond to either the trypsin or the erepsin of the animal body. It has been found that in certain cases the juices or extracts of plants can peptonise fibrin, indicating the presence of a tryptic protease; but more commonly they do not possess this capacity. The following are instances of the peptonisation of fibrin :-- Pine-apple (juice); papaïn (solution); nepenthes (pitcher-liquid); yeast (extract); mushroom (extract); cucumber (juice); melon (juice); wheat-germ (extract); asparagus (juice); Phytolacca decandra (extract of leaves); fig (extract of leaves). It may be inferred that a tryptic protease is present in these plants. It is not necessary to give a list of cases in which peptolysis of albumoses and peptones (as contained in the commercial preparation known as Witte-peptone) has been observed; it appears that the juice or watery extract of almost any part of any plant can effect this process. Although fibrin is not digested in these cases, yet any proteid matter naturally present in the juice or extract is digested autolysis). Hence it may be inferred that an ereptic protease is present. I have found in the yeast and the mushroom that both a tryptic and an ereptic protease are present; no doubt other cases of such an association of proteases, analogous to that of the 'trypsin' of animals, remain to be discovered. It may be stated generally that these proteases are most active at the natural degree of acidity of the juices or extracts. It is, however, quite possible that the protease here described as 'tryptic' may be found to be a mixture of erepsin with a pepsin. 4. Sexuality in Zygospore Formation. By Dr. A. F. BLAKESLEE. 1. The production of zygospores in the Mucorineæ is conditioned primarily by the inherent nature of the individual species, and only secondarily by external factors. 2. According to their method of zygospore formation, the Mucorinese may be divided into two main groups, which have been termed respectively homothallic and heterothallic. 3. In the homothallic group, comprising the minority of the species, zygospores are developed from branches of the same thallus or mycelium, and can be obtained from the sowing of a single spore. 4. In the heterothallic group, comprising probably a large majority of the species, zygospores are developed from branches which necessarily belong to thalli or mycelia diverse in character, and can never be obtained from the sowing of a single spore. 5. These sexual strains in an individual species show in general a more or less marked differentiation in vegetative luxuriance, and the more or less luxuriant may be appropriately designated by the use of (+) and (-) signs respectively. 6. In heterothallic species, strains have been found which from their failure to react with (+) and (-) strains of the same form have been called 'neutral,' and a similar neutrality may be induced by cultivation under adverse conditions. 7. In all species of both groups in which the process of conjugation has been carefully followed, the swollen portions (progametes) from which the gametes are cut off do not grow toward each other, as currently believed, but arise from the stimulus of contact between more or less differentiated hypha (zygophores), and are from the outset always normally adherent. 8. In some species the zygophores have been demonstrated to be mutually attractive (zygotactic). 9. In the heterogamic subdivision of the homothallic group a distinct and constant differentiation exists between the zygophoric hypha and the gametes derived from them, but in the remaining homothallic forms and in all heterothallic forms no such differentiation is apparent. 10. A process of imperfect hybridisation will occur between unlike strains of different heterothallic species in the same or even in different genera, or between a homothallic form and both strains of a heterothallic species. 11. By taking advantage of this character it has been possible to group together in two opposite series the strains of all the heterothallic forms under cultivation. 12. When thus grouped the (-), or less luxuriant strains, will be in one series, while the ( + ), or more luxuriant, will be in the other. 13. From the foregoing observations it may be concluded : (a) That the formation of zygospores is a sexual process; (b) That the mycelium of a homothallic species is bisexual; (c) While the mycelium of a heterothallic species is unisexual; (d) And, further, that in the (+) and (-) series of the heterothallic group are represented the two sexes. 5. Some General Results on the Localisation of Alkaloids in Plants. By Professor L. ERRERA. Microchemistry does not claim in any way to supplant chemistry. Its great value consists in permitting an approach to problems unattainable by ordinary analytical methods, and in accomplishing for physiological (and also for petrographic) chemistry the work of penetration and localisation which the microscope performs for structure. For a long time botanical microchemistry has dealt with a limited number of bodies and reactions: cellulose, starch, reducing sugars, inulin, proteid matters, asparagin, tannins, silica, and calcium compounds. Gradually a series of interesting bodies have been added to the original scanty list, such as sulphur, glycogen, salts of iron and other bases, alkaloids, myrosine, certain glycosids, prussic acid, &c. Although a few valuable preliminary researches had already appeared, a more methodical attempt to localise, in the various tissues, the important group of alkaloids was made in a paper I published in 1887 in collaboration with two of my pupils, Dr. Maistriau and the lamented Dr. Clautriau. We used a great number of general as well as special reagents of the different alkaloids which we examined, for the sake of their mutual control. In consequence of the fact that many alkaloids are closely related to proteids, a great analogy exists in the action of many general reagents on both classes of compounds. This is, of course, a serious difficulty in microchemical determinations. But an alcoholic solution of tartaric acid separates clearly the two groups, dissolving the former from the cells and leaving the latter undissolved, and this method has always given very good results. Similar lines of investigation have been followed with success within the last eighteen years by a number of my pupils and by many other observers, principally in Holland and Sweden, but also in France, Germany, and Italy. The more important conclusions arrived at by these researches (which must, of course, be conducted critically) might be summarised as follows: (1) The qualitative and to some extent the quantitative distribution of alkaloids (especially those belonging to the pyridic series) can be determined microchemically in the various organs of plants with perfect certainty. (2) In living cells the alkaloids are eliminated from the protoplasm and gather in the vacuole. It is only in cells which have lost all their liquid contents (as in ripe seeds) or in dead cells that they accumulate in the protoplasm or the cell-wall. (3) The alkaloids are generally localised: (a) In very active tissues: chiefly in the neighbourhood of growing points (a little behind the initial cells), in the ovules, &c.; (b) In the epidermis, the epidermic hairs, often also in the sub-epidermic layers of vegetative organs, as well as the outer layers of fruits and seeds; (c) Round the fibro-vascular bundles, in certain of their phloem-elements and in the neighbourhood of the pericycle; (d) In the phellogen and the youngest cork-cells (either normal or consecutive to traumatism); (e) In the laticiferous or similar elements, when present. (4) By means of the microchemical tests many new alkaloid-plants have been discovered, the result being afterwards confirmed by the usual chemical methods, e.g. certain Orchidaceae (where alkaloids were formerly quite unknown), Amaryllidaceae, Papaveracea, Ranunculaceæ, Solanaceæ, &c. (5) Although the investigation of animal tissues is particularly delicate, observations (yet unpublished) show that even here a microchemical identification of organic bases is sometimes possible-for instance, in Salamandra. (6) Granting that the physiology of alkaloids is far from settled, I think a critical study of their topography as well as their behaviour in germination, growth, etiolation, maturation of seeds, &c., supports the view that they are waste-products, resulting from the catabolism of cytoplasm, and secondarily utilised for defence against animals. A few grams of an alkaloid constitute a protection not less efficient than the strongest spines. The diminution of the proportion of alkaloids in a given plant is often wrongly interpreted as a proof of their direct consumption as plastic material. But the |