674 SUMMARY OF CURRENT RESEARCHES RELATING TO 



rarely forms new tissues, but it may be the seat of the formation of 

 adventitious roots. 



The recognition of the pericycle as a distinct element in the con- 

 stitution of the root, stem, and leaves, greatly facilitates the distinc- 

 tion between the central cylinder and the cortex. The innermost 

 layer of the cortex is the endoderm ; but this frequently loses the 

 special characters by which it is ordinarily distinguished, and the 

 boundary of the cortex can then be determined by the pericycle, which 

 is always recognizable by the presence of scleric elements and by its 

 generating power. It also serves to define more exactly the position 

 and constitution of the liber. To this latter have frequently been 

 erroneously referred certain lignified elements which really belong to 

 the pericyclic layer between the outermost portion of the bundles and 

 the endoderm. Furthermore the recognition of this structure permits 

 the place of formation to be exactly defined of elements hitherto 

 referred to various anatomical regions. A good illustration of this 

 is afforded by Van Tieghem's observations * that the oleiferous canals 

 of Umbelliferee, Pittosporeae, and Hypericum, originate in the peri- 

 cycle, equally in the root, stem, and leaves ; while the laticiferous 

 vessels of Cichoriaceas have their origin in the pericycle in the stem 

 and leaves, in the liber in the root. 



Changes of Structure in Land -Plants when growing sub- 

 merged."!" — Herr H. Schenck describes these changes, which are espe- 

 cially pronounced in the case of Cardamine pratensis when growing 

 entirely submerged in water. They are all in the direction of the 

 structure of the organs and of the tissue in plants which grow ordi- 

 narily beneath the surface of the water. The leaves acquire long 

 stalks ; the mechanical elements are greatly reduced ; the cuticle of 

 the epidermis being thin, and the fibrovascular bundles reduced in 

 size, especially the xylem. On the other hand, the assimilating tissue 

 of the leaves is much more strongly developed, the cells of the 

 mesophyll being rounded and very loosely associated. 



Epidermis of the Leaves of Aquatic Plants.J — M. J. Costantin 

 disputes the statement of Brongniart and Jussieu that the leaves of 

 aquatic plants are destitute of an epidermis. This statement rests on 

 the hypothesis that epidermal cells do not contain chlorophyll, and 

 that the leaves of aquatic plants do not possess stomata ; but the 

 author points ou:t that both these assertions can only be accepted with 

 a considerable amount of exception. He states also that the number 

 of stomata varies in leaves of precisely the same character in the same 

 species, and that the water surrounding the leaves has a direct 

 influence on the formation of stomata. 



Structure of B,anunculacese.§ — M. P. Marie has made a close 

 examination of the structure of the different organs in the various 

 genera and subgenera of Eanunculacese, which he describes in detail, 



* See this Journal, iv. (1884) pp. 767-70. 



t Ber. Deutsch. Bot. Gesell, ii. (1885) pp. 481-6 (1 pi.). 



X Bull. Soc. Bot. France, xxxli. (1885) pp. 83-92. 



§ Ann. Sci. Nat.— Bot., xx. (1885) pp. 5-180 (8 pis.). 



