r 



1 902] CURRENT LITERATURE 73 



^ of the Porphyra plant, analogous to the Chantransia condition of Batracho- 



spermum. It is a very advantageous adaptation to insure the continuous 

 production of numerous fronds. No new facts are presented respecting the 

 problem of sexuality in this group, but the observations are rather against 

 the statements of Berthold. — B, M. Davis. 



In a second paper on the influence of tensions upon cell growth and 

 the direction of new walls Kny^^ concludes that when no other factors are 

 effective, growth takes place in the direction of a pull and at right angles to 

 that of a compressing force. Cross walls seek a direction perpendicular to 

 external pressure upon the dividing cell, but parallel to a stretching tension 

 exerted upon it. There are '* internal forces" at work in most living tissues, 

 which tend to prevent this reaction to tensions, *' heredity'' being apparently 

 the main one. This means, if we judge correctly, that the above principle 

 does not nearly always hold true, but that the direction of growth and of 

 I wall-formation is mainly controlled by as yet unknown factors. Perhaps the 



most definite result of experimentation here recorded is one obtained, at the 

 suggestion of the author, by M. Nordhausen on segmenting eggs of Fucus. 

 Although the first walls in these eggs are normally formed at right angles to 

 mcident light, when the eggs are compresse4 between glass plates these walls 

 always appear perpendicular to the plates, no matter if this direction be par- 

 allel to the incident light rays. Kny experimented upon roots of Vicia, 

 Malva, Raphanus, tubers of Ullucus, and stems of Impatiens, Begonia, Bryo- 

 phyllum, Ampelopsis, Salix, etc. Two plates showing the effect of tensions 

 upon the different tissues accompany the paper. — B. E. Livingston. 



Dr. D. H. Scott '9 has recently published an account of some interesting 

 fossd stems, chiefly from the Lower Carboniferous of Scotland. Although 

 the specimens described have the Dadoxylon or Araucarioxylon type of 

 secondary wood, they differ strikingly from other known stems of Cordaites in 

 the possession of mesarch bundles of primary xylem. The fossils are grouped 

 under three genera. Calamopitys, Pitys, and Dadoxylon. Calamopitys is char- 

 acterized by a small pith, surrounded by a few comparatively large mesarch 

 primary wood bundles, and a thick zone of secondary wood. Pitys possesses 

 a very large medulla and numerous mesarch primary strands, which are 

 separated from the secondary wood by a broad interval of parenchyma. Of 

 the third type of stem, Dadoxylon Spenceri, Dr. Scott writes : " The impor- 

 tance of Z>. Sp€7iceri lies in its being on the one hand a typical Dadoxylon, 

 with the type of secondary wood which we know belonged to Cordaites, while 



Kny, L., Ueber den Einfluss von Zug und Druck auf die Richtung der Scheide- 

 wande in sich theilenden Pflanzenzellen (Zweite Mittheilung). Jalirb. Wiss. Bot. 

 37:55-98. 1901. 



'^On the primary structure of certain Palaeozoic stems with the Dadoxylon type 

 wood. Trans. Roy. Soc. Edinburgh 40' : 331-365. ph, 2-6. IQ02. 



