1917] DUNN—DUMONTIA 451 



structure as those in the mature tetraspores. The majority of 

 carpospores in a mature cystocarp contain one large nucleus each 

 (fig. 66). Occasionally a spore which is just about to escape con- 

 tains 2 nuclei (fig. 67). The spore shown in fig. 67 was directly 

 behind a spore which was just passing through the pore in the wall 

 of the cystocarp. The fact that the nucleus divides in some of 

 these carpospores just as they are escaping indicates that the spores 

 germinate as soon as they are discharged. In fact, the spores 

 sometimes germinate while still inclosed in the cystocarp. In most 

 of the female plants collected, the tips of the main axis of the thal- 

 lus and branches were frayed out. The mature carpospores are 

 present at these points, and it is therefore evident that the dis- 

 integration of the cells surrounding them furnishes one possible 

 means of escape. As the carpospores enlarge, they compress the 

 surrounding vegetative cells on all sides, and also cause the wall 

 of the thallus to bulge out. The layers of cortical and subcortical 

 cells gradually become thinner on the bulging side of the pericarp, 

 until finally they are ruptured and the naked carpospores escape 

 through the pore thus formed (fig. 68, 1). 



Groups of multinucleate cells, which are of the same size and 

 have the same position as the normal cystocarps, occasionally 

 occur in the wall of the thallus. In group 1, fig. 68, a section of a 

 normal cystocarp, 16 spores appear to be present, but probably 

 not all of these are in this one cystocarp. Similar sections of two 

 groups of multinucleate cells on the other side of the thallus (2 

 and 3) contain respectively 30 and 70 cells. Some of the cells in 

 the groups of multinucleate cells are uninucleate and of the same 

 size as the mature carpospores (fig. 66), while others of approxi- 

 mately the same size or smaller contain 2 or 3 nuclei (figs. 67, 69, 

 71). In some cases nuclear division is followed by cell division 

 (fig. 70). Evidently after one of these larger spores divides, the 

 daughters may in turn become multinucleate (fig. 71). From the 

 arrangement of some of the cells it appears as though the larger 

 cells have divided to form the smaller ones. The number of nuclei 

 in the cells of a cystocarp similar to group 3, fig. 86, does not seem 

 to be determined by the size of the cells. Some of the smaller 

 cells may contain as many as n nuclei and the larger ones only 



