1 48 Biologie. — Physiologie. 



internal phloem or endodermis is to be observed. Such cases 

 as these are regarded as examples of the degeneration of a 

 typically concentric stclar tube. 



Among the Lycopodiales a tubulär central cylinder without 

 any foliar gaps is held to occur in Tmesipteris, Psilotiun and 

 Phylloglossum, also in Selaginella laevigata and certain Lepi- 

 dodendrons, where however ramular gaps are to be observed. 

 The author favours the hypothesis that the vascular System of 

 Lyginodendron, and of the Cycads, has been derived b\ 

 reduction and specialization from polystelic ancestors, and 

 comes to the conclusion that the medullated monostele of the 

 Gymnosperms and Angiosperms has also descended from a 

 siphonostelic condition with complete degeneration of the 

 internal phloem and endodermis, and that therefore the pith is 

 always to be regarded as belonging to the fundamental tissue. 



The results are finally summarized by the conclusion that 

 there are two types of cauline central cylinder; (1) the proto- 

 stele, vvhich is the more primitive, and consists of a Single con- 

 centric vascular Strand without a medulla; (2) the siphonostele. 

 which is tubulär with a medulla derived from the fundamental 

 tissue, and is characterized by the presence of ramular lacunae 

 only, or by both ramular and foliar lacunae. Cases in which 

 the siphonostele ceases to be obviously tubulär in the adult 

 may be termed adeiosiphonic. 



The siphonostele is primitively concentric but in Angiosperms, 

 Gymnosperms etc. it has become collateral by reduction. The 

 pith is to be regarded as an inclosed portion of the fundamental 

 tissue. 



There are two phyllogenetic types of siphonostele. The 

 eladosiphonic, with ramular gaps only and the phyllosiphonic, 

 with both ramular and foliar gaps. The Vasculares may be 

 divided between these two types. The Lycopsida, including 

 the Lycopodiales and Equisetales, are eladosiphonic, and the 

 Pferopsida, including the Fi/ica/es, Gymnosperms and Angio- 

 sperms are phyllosiphonic. D. J. Gwynne-Vaughan. 



Friedel, Jean, Formation de la chlor ophylle dans I'air 

 rarefie et dans l'oxygene rarefie. (Comptes rendus 

 de l'Academie des sciences de Paris. (8 Decembre 1902.) 



Les experiences ont porte sur !e Lepidium sativum et le 

 Phaseolus multifloriis. 



Dans l'air rarefie ä x /ö ou ' e d'atmosphere, ces plantes 



restent etiolees; dans de l'oxygene pur a la meme pression, 



elles verdissent autant que les plantes temoins inaintenues ä 

 l'air libre. 



Dans de l'air tres pauvre en oxygene, oü l'on absorbe le 

 gaz carbonique au für et ä mesure de sa produetion, les 

 plantes ne verdissent pas. La pression totale semble n'avoir 



