1917] DUNN—DUMONTIA 435 



carpospores persist through the winter. These holdfasts, in the 

 following June, produce adventitious shoots which develop into 

 tetrasporic plants. Lewis believes that this is in general the 

 seasonal cycle of many of the Florideae, but states that "there are 

 also exceptions to the separation in point of time of the two 

 generations. This separation is never of a perfectly sharp and 

 definite character, as the generations always overlap to a certain 

 extent in midsummer." 



The seasonal cycle of Dumontia at South Harpswell is evidently 

 not similar to that of the algae just mentioned. The carpospores 

 discharged in May and June apparently develop immediately into 

 the tetrasporic plants which are present in June and July. This 

 seems clear from the fact that the carpospores sometimes germinate 

 even before escaping from the cystocarp, also that young tetrasporic 

 plants 3-7 cm. in height were often found growing beside the stumps 

 of the frayed off cystocarpic plants. Germination of the tetraspores 

 has not been seen, but the occurrence of only male and female 

 plants in the spring would indicate that this species must persist 

 through the winter in the form of sporelings derived from the 

 tetraspores discharged in June and July. 



VEGETATIVE STRUCTURE 



The holdfast of Dumontia is a platelike body composed of a single 

 layer of horizontal filaments, each cell of which produces an ascend- 

 ing, vertical branch (figs. 8, 9). These vertical branches are closely 

 packed together, averaging about 12 cells in length, and are very 

 regular in form and arrangement. They are generally dichoto- 

 mously branched. The cells of the horizontal filaments usually 

 form no descending branches. The few branches of this character 

 observed consisted of only one cell (fig. 8). It is evident from the 

 size and arrangement of the cells in the ascending branches that 

 they develop by apical growth. 



A group of vertical branches in the holdfast elongates to form 

 the upright portion of this alga (fig. 9). In such longitudinal fila- 

 ments there is a gradual increase in the length of the cells. They 

 are closely packed together at the base of the main axis, forming 

 a solid tissue (fig. 9). At about 0.1 mm. above the holdfast these 



