52 



Harvey^), to be due to an apical cell, but this is not right, 

 judging from what I have found in my material. The cell-divi- 

 sion is namely carried out by segregative cell-division. I have 

 observed the cell-division in the frond of a young plant, of which 

 Fig. 38 c shows the uppermost halfpart. We see here that the 

 side branches and the apical cell first grow out to a considerable 



length (compare al- 

 so Fig. 38 a, b) and 

 then the cell con- 

 tents in each branch 

 are divided simul- 

 taneously into a 

 number of smaller 

 parts of nearly the 

 same size, with ex- 

 ception of the apical 

 part in each branch, 

 which is longer. 

 Each of these smal- 

 ler parts becomes 

 surrounded by a 

 membrane. The 



figure shows that 

 the branches nearest 

 the top are yet 

 undivided. Some- 

 what lower down, 

 where the division 

 of the contents has 

 recently begun, we 

 find that the single 

 parts of the contents 

 are separated from 

 each other by a 

 rather large open 

 space, larger per- 

 haps owing to the influence of the alcohol than in the living plant. 

 These parts are surrounded by a membrane and then, as we see in 



Fig. 38. Struvca elegans Borgs. 

 a, h, c, tops of young stalks showing development 

 of the frond and c the cell division also, the 

 uppermost branches in this figure and the top- 

 cell are yet undivided, then branches occur where 

 the cell contents are aggregated in clumps and 

 lower down again the cell-division has been com- 

 pleted and in the lowest pair of branches new 

 side branches begin to grow out. d, part of older 

 thallus. e, /, hapterae. g, chromatophores. (a, b, 

 about 3:1; c, 6:1; d, IU:1; e, /, 70:1; g, 300:1). 



^) Compare also Murray and Boodle, I.e.; Oltmanns, Morphologie, 

 p. 267; WiLLE in Engler und Prantl, Natiirl. Pflanzenfam., Chloro- 

 phyceae, Nachtr., p. 113. 



