1G2 FUESU-WATKU A L G .E O K THE UNITED STATES. 



instead of a connecting tnbc being formed as the medium of union, two cells of 

 opposing lilanients become sharply bent backwards, so that their central portions 

 arc strongly thrust forward as obtuse points, which, coming in contact, adhere and 

 allow of a passage-way between the cells being made by the absorption of their 

 cohering walls. 



A curious modification of, or departure from, the ordinary method of conjugation 

 is sometimes seen, in the union of three instead of two cells. This is, I think, 

 very rare, but has been seen by Meyen in the genus Zijynema, as well as by 

 Schleiden and Ue Bary in Sj^nrogyra. I myself have observed it once or twice iu 

 the latter genus. One of the cells plays the part of the female, receiving the con- 

 tents of the other two, so that in it the primordial utricles of the three, with their 

 contracted protoplasm, arc fused into a zygospore. 



The zygospore, however formed, varies in shape, but is mostly oval or globular, 

 sometimes cylindrical, and when ripe is in most if not all species of a dark brown- 

 ish color. It is described both by Pringsheim and De Bary as having three coats, 

 but I luu e frcfpiently found it impossible to demonstrate the presence of all of 

 these, and I believe that not rarely one of them is absent. The outer coat is 

 developed first and is the thickest and firmest. Occasionally it is double, i. e. 

 composed of two distinct layers or parts, as in /S/>. 2^^ot€''fa, iu which species the 

 outer of these layers is the thickest, firmest, and most evident, whilst the imier 

 layer is translucent and much less apparent. The second coat contains the 

 coloring matter, which is sometimes brown, sometimes decidedly yellowish. The 

 inner coat is not readily seen. It is elastic, thin, and is the last of the three to be 

 formed. 



The princii)al contents of the ripe spore are protein compounds (protoplasm), 

 oil-drops, starch granules, and pigment. The oil is generally much more abun- 

 dant than the starch, and not rarely the minute, bright drops entirely replace 

 the little granules. According to Prof. De Bary, the pigment frequently, but not 

 always, reacts Avith sulphuric acid, as does that of the fungal family, Urcdinece, 

 striking with it a deep blue. 



The germination of the spore, both in the genus Spirorjyra and Zijfjnema, is 

 very simple. The first step is an elongation and growth of the protoplasmic 

 central mass, together with the inner transparent cellulose coat, and a consequent 

 rupturing of the outer two coats, through which the newly forming plant protrudes 

 and finally escapes. In this way in the genus Splrofjijra an elongated club-shaped 

 cell arises, one end of which is much larger than the other and contains all the 

 chlorophyl. Sometimes a nucleus is perceptible in this cell, sometimes it is not. 

 The larger end now becomes cut oft' by a partition Avail from the smaller; if no 

 nucleus has been previously apparent it noAv becomes so, and the first stage of 

 development is completed. Tlie filament after this grows by a simple repetition 

 of the process of division in th(> larger end and the cells formed out of" it. The 

 smaller end undergoes little or no change. In the genus Z[i<jnema, the cell that 

 first emerges from the germinating spore is a perfect one, similar in all respects to 

 those seen in tln^ fully formed filament, which is developed out of it, by a simple 

 process of cell division. 



