BOOKS AND CURRENT LITERATURE 283 



defined species now passing under the name of Hariota salicornioides, 

 but Lofgren recognizes only two varieties here. Pfeiffera does not 

 resemble very closely in its habit, flower or fruit any of the species of 

 Rhipsalis, and onlj^ on account of its small flowers does it suggest 

 Rhipsalis. Dr. Lofgren refers to his subgenus Pfeiffera also Rhipsalis 

 pilocarpa, on account of its pilose ovary and fruit; but we do not be- 

 lieve it is congeneric with Pfeiffera or Rhipsalis. In its habit it looks 

 mere like Rhipsalis proper than Pfeiffera; but in its tubular flower, 

 inner perianth segments, style and ovary, is quite different. — J. N. 

 Rose. 



Mitosis. — In a recent paper' Karsten gives the results of studies 

 on the relation of the frequency of mitosis to hght and darkness. He 

 finds that the greater frequencies occur in the dark, both in the root 

 and in the shoot. He finds also a fixed daily periodicity, the maxi- 

 mum nmiiber of mitoses occurring between 7 and 11 p. m. Karsten 

 appears to be entirely ignorant of Kellicott's work,^ done 12 years ago 

 and leading to the same conclusion. The more recent work on the 

 relation of growth to light, temperature and transpiration indicates 

 that any generalizations on the relation between elongation or other 

 extension of growing parts and mitosis, especially when based on the 

 Sachs dictum, quoted by Karsten, is open to criticism .-^F. E. Lloyd. 



' Karsten, G., tjber embryonales Wachstiim und seine Tagesperiode. Zeitschr. 

 f. bot. 7: 1-34. 1915. 



^Kellicott, W. E., The daily periodicity of cell division and elongation in the 

 root of Allium. Bull. Torr. Bot. Club 31: 1904. 



