1912] BARRETT— BLAST0CLAD1 A 359 



empty zoosporangia may be seen still attached to the plants weeks 

 after they have ceased to produce reproductive organs. 



As growth of the zoosporangium proceeds, there is a noticeable 

 condensation of the protoplasm in the center, around which can be 

 seen a number of indistinct vacuoles of irregular shape. There is 

 little apparent change from this condition until the zoosporangium 

 has reached its maximum size. The contents then become coarsely 

 granular and no vacuoles are apparent. This stage may persist for 

 some time if conditions for further development become poor. In 

 fact, it is in this stage that zoosporangia rest at times for days. 

 Suddenly the coarse granular character changes to one with fine 

 evenly distributed granules, and the whole contents assume a much 

 lighter appearance. After 1 5-30 minutes one can discern the for- 

 mation of areas surrounded by faint granular but irregular lines. 

 These become rapidly more prominent, and in a few minutes a 

 slight movement can be detected within the zoosporangium. The 

 areas represent the zoospores and their discharge is about to take 

 place (fig. 8). The papillae of dehiscence, sometimes numbering 

 as many as eight, become more and more extended and refractive 

 until one or more finally break open, permitting the zoospores to 

 escape. They pass out in single file, at first rather rapidly, then 

 more slowly as the pressure within the zoosporangium becomes 

 lessened (fig. 56). Being of a plastic nature, they squeeze through 

 the opening, arriving at the outside irregular in form, and very 

 commonly with their cilium held in the opening by the next 

 emerging zoospore. After a few seconds they move slowly away, 

 assuming their normal form. - 



The zoospores are oval to elliptical, not infrequently slightly 

 ovate, in which case the narrower end is the anterior one. The 

 number of cilia varies from one to three, and they are attached at 

 the posterior end. From a large number of careful examinations 

 of both living and stained preparations of zoospores, I assume that 

 the uniciliated condition is the typical one, as it occurs much more 

 frequently than the other two types. The triciliated zoospore is 

 rarely seen, while the biciliated form is common. The zoospores 

 of B. Pringsheimii possess, according to Thaxter (9), one or two 



