ZYG0SP0R^T5. 1 7 



explanation of these movements has yet been given. To some 

 they appear a mystery, but, are they more mysterious than the 

 circulation of blood in our arteries and veins, or than that of the 

 so-called cyclosis in the higher plants? Xearly, if not quite all 

 vegetable germinal matter, displays some spontaneous activity, 

 and it is more than probable that the like characteristic seen in 

 the Desmids, must be ascribed to the same causes whatever they 

 may be. 



MULTIPLICATION. 



Multiplication among the Desmids takes place by two pro- 

 cesses. The one is simply a division and growth, the other is 

 through what may be termed sexual intervention. 



The first process is merely a modification of ordinary vegeta- 

 tive growth, that is to say, a peculiar cell multiplication by 

 division. Plate XV, figs. 5, 6, are two semi-cells of a Docidium, 

 which have separated by the development of short processes 

 (fig. 7) ; these, primarily very small, commence their growth 

 from out of the center of the base of each semi-cell. The figure 

 represents them somewhat advanced ; they develoiJ rapidly, and 

 soon become exact counterparts of the original mother-cells, then 

 they separate. Thus two cells are developed from one ; the same 

 process is repeated, the two produce four, the four eight, and 

 so on. 



Plate XVII, figs. 12, 13, represent a Cosmarium, the one the 

 perfect plant, the other in process of division ; the ends are the 

 halves of the mother-cell ; the parts between, the partially de- 

 veloped forms of the new semi-cells. Plate XIX, fig. 27, repre- 

 sents a similar growth of a denticulate form ; the teeth are not 

 apparent until the young parts have attained nearly their full 

 size. 



Plate XLIV, fig. 8, is a series of four Micrastet-icts truncata, 

 which represent the stages of growth by division ; a cell pro- 

 ducing two, and the two, four, under the rather unusual circum- 

 stance of adherence after division ; only a fragment of the series 

 is shown in the figure. Fig. 11 is a similar fragmentary series 

 of adhering cells which must originally have numbered no less 

 than sixty-four. I counted thirty-eight which could not have 

 occurred in a regular course of division. 



There are some peculiarities attending the process of multi- 

 plication. The new semi cells are not always exact counterparts 

 of the mother semi- cell. Plate XVIII, fig. 18, Cosmarium monili- 

 forme; here there is an enlargement of the new, central semi- 

 2 



