i.ll SUMMAKY OF CURRENT RESEARCHES RELATING TO 



thai plants, in accommodating themselves to their surroundings, change 

 their habit and the proportions and attitude of the parts of the shoot. 

 Thus the pith in correspondence with this change may arise from more 

 deeply seated or more superficial sources. 



Embedded Antheridia in Pteris.* — M. C. Ferguson describes some 

 instances of embedded antheridia in cultivated prothallia of Pteris. A 

 similar abnormality has been observed in Dryopteris and Nephrodium by 

 ('. A. Black.f Ferguson points out a few details in which her examples 

 differ from those of Black. The embedded antheridia may attain a 

 size quite six times that of the normal exserted antheridia. Ferguson 

 describes also some abnormal archegonia containing two egg-cells and 

 two ventral canal-cells lying in the plane of the longer axis of the arche- 

 gonium. She also calls attention to an instance which she figures of a 

 small archegonium in which the central cell has become developed into 

 what appears to be a sperm-cell. 



Xylem Elements of the Pteridophyta.J — N. Bancroft writes on the 

 xylem elements of the Pteridophyta. She gives the following summary 

 of her work : — 1. The xylem elements of Pteridophyta are typically 

 pointed tracheides, the pits on both end and side walls being closed by a 

 membrane formed by the persistent middle lamella. 2. The middle 

 lamella is believed to be exposed in the pit areas by the disintegration 

 of the rest of the primary wall. 3. The varying amounts of disintegra- 

 tion give rise to the prevalence of the "split" or "non-split" appearance 

 between the secondary lignified layers, as seen in transverse section. 

 4. The width of the split depends largely upon the degree of separation 

 of the secondary layers in the areas surrounding the pit openings. 



Development of Stele in Dipteris.§ — H. de Bruyn describes the onto- 

 genetic development of the stele in two species of Dipteris. Her summary 

 of her work is too long and detailed for quotation. In brief, she finds 

 that : — 1. The evolution of the stele is similar in Dipteris conjugata and 

 D. Lobbiana. 2. The central tissue in middle of xylem at first consists 

 of parenchyma ; later sieve-tubes appear and a typical Lindsaya stage is 

 reached. 3. Cells with dark contents appear here and there irregularly 

 in the central tissue. They probably represent the beginning of an 

 internal endodermis, but make no connexion with the external endo- 

 dermis till after the departure of several leaf -traces. 4. Higher up the 

 dark cell-strand is regularly connected with the outer endodermis at the 

 leaf-gaps. Eventually pith-cells appear in the centre of the group of 

 dark cells, and a normal solenostele is formed. 5. The thickening of the 

 xylem on the edges of the leaf-gap occurs in quite young as well as 

 mature plants. 6. A feature in the young plants is the irregularity of 

 development in several of the stelar "tissues. 7. The structure of the 

 leaf-traces differs in detail in the two species and indeed in different 

 petioles of the same species. 



* Bot. Gaz.. li. (1911) pp. 443-8 (2 pis.). 



t Bull. Torrey Bot. Club, xxvi. (1909) p. 557. 



X Ann. of Bot., xxv. (1911) pp. 745-59 (1 pi. and figs.). 



§ Ann. of Bot., xxv. (1911) pp. 761-72 (2 pis.). 



