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OP A STIPITATE FRESHWATER ALGA. 461 



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chlorophyll becomes aggregated on one side of the minute spheres 

 of protoplasm, which externally exhibit rotatory movements, and 

 finally escape from the cells as globose zoospores about 4/x in 

 diameter, furnished with a minute knob-like projection on the 

 colourless side of the sphere, from which originates two exceed- 

 ingly slender cilia, each about 12// in length. 



-During the period occupied in the differentiation of the proto- 

 plasm, previously concerned with vegetative work bearing on the 

 well-being of the individual, into zoospores, the mucilaginous wall, 

 as a ' so the innermost firm cellulose portion belonging to each one 

 0* the apical swollen portions, has lost its individuality and 

 blended with the common sphere of mucus. The liberated 

 zoospores are all of equal size, and after remaining active for 

 about two hours become stationary, resorb their cilia and become 

 surrounded by a wall of cellulose, during which change the 

 chlorophyll becomes equally diffused throughout the cell, which 

 18 ^ ow i& a condition to recommence the vegetative phase by 

 hssion. It is certain that many succeeding generations are 

 produced by the above method during the summer months ; as to 

 whether the ultimate zoospores become encysted, and in this 

 condition pass the winter months, I have unfortunately been 

 unable to determine. 



Although the plant under consideration is technically uni- 

 cellular, it nevertheless approaches very closely various generic 

 *ypes of freshwater algae that are probably, out of deference io 

 historic prejudice, considered multicellular. 



The most prominent morphological feature presented by the 

 species of T>ictyosph<eriwm is the repeated division of the original 

 spherical cell into portions radiating equally from a central point, 

 a »d in the persistent concentration of the protoplasm at the tips 

 of the repeatedly dichotomous radiating stem-like portions. In 

 th e last feature the present genus at first sight appears to be 

 Unique, but the difference is really but one of degree. The spores 

 °f numerous, in fact of most species of multicellular algae, both 

 freshwater and marine, aud also of many unicellular forms, on 

 germination, produce a distinctly stipitate plantlet, due to the 

 P^toplasm remaining concentrated at the apex and leaving a 

 colourless, thin, empty portion of the cell-wall behind in the 

 *orm f a 8tem _ Uke ba8e? whicb is usua lly discoid at the point of 



attachment. Such forms differ from the initial stage of Dictyo- 

 *ph<srium in the snore not at once dividing into four, but remaining 



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