ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 377 



dropsis among the Zygopteride;c, while the triarch condition may have 

 arisen by the amplification of a similar bundle into a tetrarch strand, a 

 slight reduction of this, and the fusion of the two median protoxylern 

 groups. 6. The constant endarch and concentric structure of the leaf- 

 bundle, as opposed to the varying conditions in the stele, point to the 

 former as a conservative organ. 7. The petiole at its attachment is in 

 many cases very slender, and the base of the leaf-trace presents always 

 its smallest and most compact condition. Structures are often retained 

 here which are undoubtedly very primitive. The petiole is largest at 

 the point where it first becomes free, probably for mechanical reasons, 

 and the bundle here is in its most complex form. 8. Since the tran- 

 spiration current seems to be accommodated equally by the slender trace 

 and by the large petiolar bundle of the same leaf, it is improbable that 

 it has had much influence in producing the complications of the foliar 

 vascular system. The stele and the leaf -trace have developed almost 

 independently, and the latter has had little influence in moulding the 

 former. 9. The condition found in the base of the trace in any fern 

 was probably once present throughout the whole leaf-bundle. 10. The 

 simple condition in the upper part of the leaf may possibly be regarded 

 as primitive. 11. The histological influence of the stele is sometimes 

 carried up into the base of the petiole, especially in cases of reduction, 

 where the petiolar bundle, better than the lower part of the leaf-trace, 

 retains conditions which may be regarded as primitive. 12. In the 

 Filicales, as in all other vascular plants, the leaf -trace is the seat of 

 ancestral characters. 



Anatomy of Marattia.* — G. M. Charles describes the anatomy of 

 the sporeling of Marattia alata. In brief her work is summarized as 

 follows : 1. The transition from protostele to solenostele is sudden, with- 

 out any definite medullated monostelic stage. 2. The medullary system 

 of Marattia differs from that of solenostelic ferns in origin, course of 

 bundles, and development into a cylinder. It resembles that of Psaronius 

 in its relation to leaf -traces. 3. Elongation of the stem causes the union 

 of the bundles into broad bands, and a reduction of the medullary 

 system. This emphasizes the close relation between the compact habit 

 and crowded leaves of Marattia, and the number of concentric cycles and 

 leaf -gaps in the dictyostele. 4. The occurrence and position of proto- 

 xylern varies. It may be inconspicuous or may consist of spiral or modified 

 reticulate tracheids. It may be in an exarch or mesarch position in the 

 cotyledonary node, mesarch in the protostele above the cotyledonary 

 node, and usually endarch in the strands of the older parts of the stem. 

 Similar variations occur in the leaf traces. 5. Apical meristems vary 

 from a triangular apical cell in young sporelings to meristematic groups 

 in older stems and roots. Such variation during the course of develop- 

 ment occurs in the gametophytes of Pteridophytes and in some liver- 

 worts, but is not recorded for the sporophyte of other ferns. 6. The 

 cotyledonary trace is collateral during most of its course. Later leaf- 

 traces start collateral and develop adaxial sieve-tubes in their course 

 through the cortex. 7. Secondary roots originate from vascular tissue 



* Bot. Gaz., li. (1911) pp. 81-101 (4 pis. and figs.). 



