ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 75 



tlte aerial stem of certain species of Juucus. Transitional forms between 

 the perixylematic and the collateral structure occur on the same 

 transverse section. The structure of the rhizome of different species of 

 Cyperacere shows an almost endless variety in the construction of the 

 bundles. 



Comparative Anatomy of Geraniaceae.* — From an examination of 

 14 species of Geranium, 3 of Erodium, and 3 of Pelargonium, Heir W. 

 Jannicke gives characters by which these three genera can be distin- 

 guished from one another, derived from the structure and distribution 

 of the vascular bundles in the leaf-stalk and flower-stalk. 



Anomalous Thickening in the Roots of Cycas.f — Mr. W. H. Gregg 

 finds in Cycas Seemanni, in addition to the abnormal thickenings of the 

 stem well-known in several genera of Cycadea3, similar thickenings in 

 the root. These abnormal thickenings of the root always proceed 

 from the pericambium, which consists of several layers of cells. The 

 primary thickening presents the peculiarity that the normal relative 

 positions of the xylem and phloem are reversed, the former lying out- 

 side, the latter inside. This is followed by an outer secondary abnormal 

 thickening, in which the xylem and phloem occupy their normal relative 

 position. 



Formation of Annual Rings in Wood. %— Herr G. Krabbe dissents 

 from the explanation of the formation of annual rings offered by Wieler, 

 that it is due to a difference in the supply of nutriment at different 

 periods of the year, less in the latter part of the summer than in the 

 spring. He asserts that this difference rests on no experimental basis — 

 Hartig maintaining exactly the opposite — and considers that the cause 

 of the formation of these rings is still an unsolved problem in vegetable 

 physiology. 



Mechanical system of Pendent Organs.§ — Herr A. Y. Grevillius has 

 investigated the peculiarities of structure of the mechanical tissues in a 

 number of plants, both shrubby and herbaceous, whether pendent varieties 

 or organs normally pendent. He finds their general characteristic to be 

 that the organs in question are narrower and more slender, and have 

 their mechanical system less strongly developed, and with a stronger 

 tendency to assume a central position. 



Comparative Anatomy of Roots.|| — Dr. 0. Lohrer has examined the 

 histological structure of the roots of representatives of a large number of 

 natural orders, to determine to what extent characters of this kind are 

 common to all the members of groups or families. He finds it to differ 

 in different cases. 



Members of fifteen families of Papilionaceae examined all agreed in 

 these points : — The bast is chiefly prosenchymatous ; the bast-fibres lie 

 scattered or in small groups in and above the soft bast ; their cell-cavity 

 is extremely small ; the very thick refringent cell-wall is clearly dif- 



* Abh. Senckenberg. Naturf. Gesell., xiv. (1886) 24 pp. and 1 pi. See Bot. 

 Centralbl., xxxi. (1887) p. 36. 



t Ann. of Bot., i. (1887) pp. 63-70 (1 pi.). 



J Ber. Deutsch. Bot. Gesell., v. (1887) pp. 222-32. 



§ Naturv. Students'allsk. Upsala, March 10, 1887. See Bot. Centralbl., xxxi. 

 (1887) p. 398. 



|| Wigand's Bot. Hefte, ii. (1887) pp. 1-43 (2 pis.). 



