STRUCTURE OF PROTOPLASM. 311 



wounded regions. The active protoplasm of a pollen tube is of 

 very liquid consistency. On ejection it gels, though it does so 

 slowly. Brownian movement sets in shortly after. 



Ejected masses of protoplasm from pollen tubes develop mem- 

 branes immediately on being freed. The capacity for mem- 

 brane formation persists one to two minutes. Within three 

 minutes the escaped protoplasm has become quite viscous. The 

 membrane formed is surprisingly tough. Fragments of it can be 

 dragged into the escaped plasma mass. 1 



Escaping protoplasm shows no sign of miscibility. Isolated 

 groups of inclusions exhibiting Brownian movement, after ejec- 

 tion, were carefully observed and in every instance the cyto- 

 plasmic matrix was distinctly visible. 



FUCUS. 



The eggs of Fucus develop from divisions of the contents of 

 oogonia which arise from single superficial cells of the wall of con- 

 ceptacles that cover the fruiting branches. If these oogonia are 

 teased out at a very early age they can be entered by a sharp 

 needle. Very soon, however, the outer wall (exochiton) be- 

 comes too hard to be penetrated. 



Oogonia. 



In consistency the protoplasm of young uninucleate oogonia 

 is very liquid. The wall is thick (2-4 microns), tough, and highly 

 resilient. Slightly older oogonia, but still uninucleate, also 

 possess very liquid protoplasm. Stages in development between 

 young uninucleate oogonia and almost mature oogonia can not 

 be observed, as the tough outer wall does not permit of dissection. 



Immature Ova. 



The contents of nearly mature oogonia can be squeezed out of 

 the heavy exochiton by crushing the conceptacle with tweezers. 



1 It was the intention of the writer to investigate the structure of the vacuole, 

 of which so many are produced in the growing pollen tube. Freed vacuoles hold 

 their shape even where exposed around the border of the plasma mass, apparently 

 free of surrounding cytoplasm. When punctured the vacuoles collapse imme- 

 diately. This behavior suggests that there is an enclosing membrane, and thus 

 that the vacuole is apparently not really a vacuole but a sac. (De Vries, 1885, 

 p. 467-) 



