ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 323 



No other flowers exhibit such colour changes, although pansies have a 

 tendency to do so ; most plants require a temperature of 30°-35° C. 

 before any colour change is perceptible, although their extracts when 

 treated with HCl have a tendency to reverse their colours. This is most 

 noticeable in such plants as Ajuya rejMns, Veronica Chamsedrys, etc. 

 The present work tends to show that colour-changes are due to dissocia- 

 tion phenomena, but the chemistry of Anthocyanin compounds is too 

 imperfectly known at present, to make certain of this. 



CRYPTOGAMS. 



Pteridophyta. 



(By A. Gepp, M.A. F.L.S.) 



Medullation in Pteridophyta.* — F. 0. Bower, in opposition to 

 E. C. Jeffrey's view that the pith is always an inclusion of the cortical 

 tissues in the stele, holds that the pith may be extrastelar as in rhizo- 

 matous solenostelic ferns, or intrastelar as in the Lepidodendracea?, or 

 of both kinds as in certain Ophioglossacefe. Probably an upright 

 microphyllous stock favours intrastelar medullation, and a creeping 

 megaphyllous stock extrastelar medullation. In upright megaphyllous 

 and creeping microphyllous stocks the pith may be partly extrastelar, 

 partly intrastelar, the disposition being dependent upon conditions 

 prevalent at the phylogenetic time when medullation was initiated, and 

 not being subsequently modified with a change of position of the stock. 

 In BotrycJiium Lunaria the first minute scale leaves were not found to be 

 subtended l)y any extrastelar pockets, but in connexion with the larger 

 leaves extrastelar pockets are formed. It is an open question whether 

 the endodermis is an immutable barrier between stelar and extrastelar 

 tissue. As to the descent of the Filicales, Equisetales, Sphenophyllales 

 and Lycopodiales from a common medullated ancestor, there is no evi- 

 dence in favour of it. The status of the pith of the higher Phanerogams 

 depends upon the manner of medullaiion initiated in the primitive 

 Pteridosperms, and not upon what obtains in solenostelic ferns. 



Xylem Elements of Pteridophyta.f — N. Bancroft publishes the 

 results of his researches on the xylem elements of Pteridophyta. He 

 confirms the opinion of Halft that these are as a rule pointed tracheides 

 with the middle lamella persisting as a pit-closing membrane on both 

 side-walls and cross-walls — an opinion which is in opposition to that of 

 Gwynne Yaughan. The pit-membrane was found to be present in all 

 the many genera examined, except in Pteris aquilina, where the mem- 

 brane is absent in the pits of the cross-walls. The middle lamella was 

 also found in the pits of Stigmaria and Sphenophyllnm. 



Vestigial Axillary Strands of Trichomanes.| — H. S. Chambers gives 

 an account of the vestigial axillary strands of Trichomanes javaniciim Bl. 

 Having described the composition of the stele, the meristeles which it 



* Ann. of Bot., xxv. (1911) pp. 555-74 (pi.). 



t Ann. of Bot., xxv. (1911) pp. 745-60 (1 pi. and figs.). 



X Ann. of Bot., xxv. (1911) pp. 1037-4.3 (1 pi. and figs.). 



