ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 93 



The cortex is wide, and composed of thin-walled cells ; the middle area 

 is more or less lacunar, and the outer layers of the stem seem to be of 

 the same nature as those of a stems. The corresponding petioles have 

 also a wide cortex, and a reduced xylem strand which is always monarch. 

 3. These differences of structure probably throw some light on the 

 autecology of Rachiopteris njlindrica, presumably an amphibious species, 

 the a and /3 plants being respectively its land and water ecads. 4. R. 

 (■ylindrka seems to be closely allied to Botryopteris antiqua, B. ramosa^ 

 and B. hirsuta. So far as the foliar trace is concerned, the four species 

 form a progressive series from the relatively primitive B. antiqua to the 

 tridentate types, R. cylindrka representing an intermediate term. 

 B. forensis does not appear to be very nearly related to this group of 

 British species. 5. Typical steles of R. cylindrka show some divergence 

 from the primitive condition, whether this is considered to be an endarch 

 or an exarch protostele, or an asterostele. 6. The method of separation 

 of the foliar trace in R. cylindrica affords support to the view that stem 

 and leaf represent homologous branches of a primitively undifferentiated 

 system. 



Leaf-arrang-ement in Branched Tree-ferns.* — J. C. Schoiite con- 

 tinues his studies on the arrangement of leaves in a paper on branched 

 tree-ferns and the branching of Pteropsida in- general. The principal 

 points are as follows. In one and the same fern-stem, the leaf scars in 

 the upper portions are in actual contact, while in the lower portions 

 they are widely separated. The separated scars are somewhat oval ; 

 those which touch each other are flattened at the point of contact. If a 

 leaf has become abortive owing to pressure, the neighbouring leaves 

 stretch their points of insertion over the vacant place, and thus lose 

 their symmetry. The author sees in this fact the unimportance of the 

 so-called contact for the position of the leaf, and for the development of 

 the leaves from a central position ; further, that the leaf -position is not 

 dependent on the form of insertion of the leaves, nor vice versa. In 

 those dichotomies, where the termination of the tissue is incompletely 

 developed in the saddle of the dichotomy, there are found leaves which 

 do not lie as usual at the point of crossing of two parastichs, but only 

 on one parastich. From this the author concludes that the parastichs 

 exercise no determining influence on the position of the leaves. The 

 leaf- traces of these leaves with special position run separately down in 

 the stem, and end, at any rate in part, without connexion with the 

 remaining vascular masses. This observation and those of Hugo de 

 Vries and Nestler on ring-fasciation are important, because they insist 

 on the basipetal arrangement of the leaf -traces, a necessary part of the 

 argument here developed by the author. Detailed observations are given 

 in this paper on the branching, a subject nearly related to leaf arrange- 

 ment. In two of the specimens examined there were transitions between 

 dichotomy and lateral branching ; these transitions were such that of 

 the two forks of the dichotomy one became always weaker, till at last 

 the weaker branch stood by the angle-leaf on the main stem, and the 



* Rec. Trav. Bot. N^erl., xi. (1914) pp. 94-193 (17 pis. and 17 figs.). See also 

 Bot. Centralbl., cxxix. (1915) pp. 165-6. 



