ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 429 



case in the lower angle made by the branch with the main stem in the 

 beech. He notes also that, in many trees, geotropic curvatures may be 

 established after the growth in length is fully completed. 



Anatomy of the Primulaceae. * — E. Decrock has studied in detail 

 the structure of the Primulacese, and of its sub-orders,with relation both 

 to the anatomy and to the histology of the different organs. This is 

 followed by a monograph of the genera and species (the four species of 

 Soldanella are reduced to one), and some general considerations on the 

 classification and biology of the order. The following are given as the 

 more important points of structure. 



The central cylinder of the root must be regarded as a conducting 

 fibro-vascular bundle, and not as a series of xylem-bundles and phloem- 

 vessels. This bundle exhibits n centres of xylem-differentiation, and n 

 centres of phloem-differentiation. The morphological value of the stem 

 as an axial organ is not the same as the morphological value of the root. 

 Sections made at the summit of the stem never show a sharply defined 

 central cylinder. At this zone the conducting system of the stem is 

 always a direct continuation of the foliar traces. There is no dis- 

 tinction between primary and secondary xylem in the stem ; the primary 

 vessels are differentiated at the expense of a cambium with tangential 

 septa, and not at the expense of procambial cells. 



C4) Structure of Organs. 



Relationship between the Length of the Stem and of the Leaves in 

 Coniierae-t — R- Meissner discusses the peculiarity displayed by many 

 conifers that there is no positive relationship between the length of the 

 branch and that of the leaves which it bears, longer shoots often bearing 

 shorter leaves, and vice versa. Ke explains this by the observation that 

 the period of strongest growth in the leaves does not coincide with the 

 period of strongest growth in the stem ; hence the climatal conditions 

 may be more favourable during the most active period in the growth of 

 the leaves than during the most active period in the growth of the stem, 

 and vice versa. 



Forms of Leaves.:}: — Prof. E. Warming illustrates the statement 

 that there are three factors which give to leaves their various forms, — 

 their physiological work, the conditions of their environment, and their 

 parentage. He takes a number of examples, mostly from climbing 

 plants, and those which grow in the deep shade of other plants. With 

 a few exceptions (Vicia, &c), the leaves of climbing plants are broad, 

 cordate, and acuminate, and are so placed that the position of the lamina 

 is vertical. 



Theory of Phyllotaxis. § — H. Winkler discusses the different the- 

 ories — the contact (Anschluss) theory, the theory of pressure, and the 

 teleological theories — which have been proposed to account for the 

 phenomena of phyllotaxis, and decides that no one of them is adequate 

 to explain the observed facts. He does not propose any alternative 



* Ann. Sci. Nat. (Bot.), xiii. (1901) pp. 1-199 (40 figs.). 

 t Bot. Ztg., lix. (1901) l ,e Abt., pp. 25-60 (1 pi.). 



j Overs, k. Dansk. Videcsk. Selsk. Forhandl., 1901, pp. 5-49 (11 figs.) (French 

 resume). § Pringsheim's Jahrb. f. wiss. Bot., xxsvi. (1901) pp. 1-79 (4 pis.). 



