TRANSACTIONS OF SECTION D. G47 



The author is of opinion that these principles may be applied to the explanation 

 of the various nyctitropic positions of motile foliage-leaves. Leaves which fall at 

 night do so in consequence of epinastic tension ; tliose which rise at night do so in 

 consequence of hyponastic tension. The horizontal diurnal position of these leaves 

 is due to the overpowering of epinasty or hyponasty by diahehotropism and 

 diageotropism acting together. 



The paraheUotropism exhibited bv some foliage-leaves, whether gi'owing or 

 motile, is referred to a special parahehotropic irritability, the reaction under the 

 influence of strong light being sufficient to overcome either hyponasty or epinasty, 

 as the case may be, co-operating with diageotropism. 



In conclusion the author refers to certain movements, such as the opening and 

 closing of the leaflets of Mirnosa jmdicn, and of the perianth-leaves of many 

 flowers, which are induced by variations in the intensity of light. He concludes 

 from his observations on Ilelianthus, &c., that the position assumed by dorsiventral 

 members in darkness is that which indicates their inherent tendencies of growth, 

 and he infers that the leaflets of Mimosa and the perianth leaves of those flowers 

 which close in darkness or in light of diminished intensity are hyponastic, whereas 

 the perianth-leaves of flowers which open in darkness are epinastic. lie points 

 out also that the effect of light in inducing change of position in these leaves is 

 quite independent of the direction of the incident light, and is determined only by 

 its intensity. The leaflets of Mimosa and many flowers open in light in conse- 

 quence of the induction of epinastic tension in hyponastic members ; flowers 

 which close in light do so in consequence of the induction of hj'ponustic tension in 

 epinastic members. These are instances of true photo-epinasty and photo-hyponasty, 

 as distinguished from the cases {Cucurbit a, Phaseolus) in which Detmer thought 

 something of the kind occurred ; the essential dift'erence being, that in the present 

 cases light induces a tension which is precisely the opposite of that inherent in 

 the leaf, whereas in Detmer's cases light merely rendered possible, by inducing 

 phototonus, the external manifestation by growth of the inherent condition of ten- 

 sion of the leaves. 



3. On some recent Progress in our Knowledge of the Anatomy of Plants. 

 By D. H. Scott, M.A., PhD., F.L.8. 



Anatomy in plants inseparable from histology ; the finer histology, however* 

 excluded from the present paper. 



Work of Grew and Malpighi laid the foundations of vegetable anatomy in the 

 seventeenth century. 



Recent progress, especially since the publication of De Bary's work in 1877, the 

 subject of this paper. 



Classification of tissues. Anatomical, developmental, and physiological methods 

 of classification. 



The Dermal Tissues. — Discoveries of Westermaier, F. Darwin, and Ilaberlandt. 

 Olivier's investigation of the primary and secondary dermal structures in roots. 

 Roots aa respiratory organs. 



The AsdmUating Tissues. — Effect of light on structure. Observations of Stahl 

 and Pick. 



The Mechanical Tissues. — Schwendener's principles not generally applicable to 

 Dicotyledons. 



The Secretory Tissues. — Ilelation of secretory sacs to laticiferous tubes. Func- 

 tions of the latter. Development of intercellular secretory spaces. 



The Vascular Bundles. — BicoUateral bundles and medullary phloem. Plasticity 

 of dicotyledonous structure. 



Secondary Grraivth. — Its importance as a means of renewal, as well as of in- 

 crease of tissues. 



Erroneous view of De Bary and Van Tieghem as to the mode of action of extra- 

 fascicular cambium. The development of phloem- islands imbedded in the wood. 

 Connection between anomalous structure and habit. Importance of the pericycle. 

 Morot's investigations. 



