264 University of California Publications. [Botany 



of the nucleus into a few thread-like masses. In these respects 

 it more nearly approaches the nucleus of higher plants than any 

 other form studied. This is the only species of this genus which 

 I was able to differentiate so sharply. Not every collection of 

 this species showed the same structure. This indicates the break- 

 ing up of the type into several species, some of which are more 

 highly differentiated than others. The measurements given for 

 the species cover a greater range than one finds in a single collec- 

 tion. This case illustrates how some of the discrepancies may 

 have arisen in the accounts of workers on the group. 



The second type, the Net-karyosome type, is quite rare. I 

 have come across but two well marked cases so far. These are 

 found in the genus Dermocarpa, two species of which I have 

 worked upon, viz., D. fucicola and D. prasina, the former of 

 which is represented by Fig. 33. This type, with perhaps some 

 modifications, will probably be found to be characteristic of all 

 the forms of Chamaesiphonaceae, which reproduce in a similar 

 manner to Dermocarpa. The type is characterized by having the 

 chromatin united into a very definite fine network on which, par- 

 ticularly at the junction of the threads, are small granules or 

 knots, presumably of chromatin, since they stain like the re- 

 mainder of the thread. This whole network occupies a very large 

 part of the cell, leaving only a narrow zone outside next to the 

 cell-wall. Material of Dermocarpa killed in Flemming's mixture 

 and sectioned does not differentiate satisfactorily with the nu- 

 clear stains. Aqueous methylene blue and Ehrlich's haematoxy- 

 lin yielded fine results on material killed in potassium iodide- 

 iodine. 



The spores of Cylindrospermum have the chromatin arranged 

 in very nearly the same manner as it is in Dermocarpa. I have 

 not come across any forms yet in which there are granules on the 

 thread, and the thread is not formed into quite so definite a net- 

 work as in Dermocarpa. Figs. 19, 20, and 21 show the condition 

 of the chromatin in the spore of Cylindrospermum. • It seems that 

 in the genus Cylindrospermum we have a transition between the 

 first and second types, the nucleus in the vegetative cells on one 

 side approaching the first type and on the other side that in the 

 spores approaching the second type. 



