Tlmherlahe — Swarm-Spores of Hydrodictyon. 497 



membrane is retained as a portion of the plasma membranes 

 of the new cells so that it is in a sense a permanent structure. 

 But it performs an entirely new role and the identity of the 

 vacuole is as completely lost as if the membrane itself were 

 destroyed. 



The production of artificial yacuoles by PfefPer (19) and 

 more lately by Xemec (18) throws little light on the real prob- 

 lem as to the origin of the yacuole, for it is not at all certain 

 that the vacuoles that were apparently formed anew were not 

 already existing, except in those cases described by Pfeffer 

 where the so-called food yacuoles in some of the slime molds 

 « may arise as invaginations of the outer plasma membrane. 

 This identity in character of vacuolar and plasma membrane's 

 so shoym^ is important when taken in connection with the fact 

 shown in various Ascomycetes and Phanerogams that the latter 

 membrane is formed by a direct metamorphosis of the kino- 

 plasmic fibres. In various Phanerogamic cells I have shown 

 that the young cell plate splits and the halves become partly 

 separated before the plate has reached the mother cell mem- 

 brane (27). This fact may furnish a suggestion as to the pos- 

 sible method of origin of vacuoles, for the cleft in the cell plate 

 is essentially a flat vacuole surrounded entirely by the pro- 

 toplasm of the motlier cell, and enclosed by a membrane derived 

 from the spindle fibres. The fact that its membrane finally 

 forms a part of the plasma membrane of either daughter cell 

 may be compared to the history of the membrane of the central 

 vacuole in the cleavage of Hydrodictyon and in those fungus 

 sporanges in which the cleavage is partly accomplished by 

 means of numerous small angular vacuoles. To be sure the 

 vacuole formed by the splitting of the cell plat« may be consid- 

 ered a very special structure without any relation to the other 

 vacuoles of the cell. But the analogy just pointed out may 

 prove suggestive as to a possible line of investigation in connec- 

 tion "\v^ith the question of the origin of vacuoles in other cases. 

 The structure and division of the nuclei of Hydrodictyon is 

 in the main features the same as that of the nuclei of the higher 

 plants. In general there are one or more fairly prominent 

 nucleoles that take a bright red color in the triple stain, and a 



