CONJUGATION OF SPIROGYBA. 



291 



We will now proceed with the examination of examples of 

 the asexual and sexual processes amongst the Algae. 



Conjugation of Spirogyra. Opportunity often offers for ex- 

 amining the various species of Spirogyra in process of Conju- 

 gation, 1 This state is recognisable out of doors by the crinkled 

 look (rather yellowish) and hanging together of their masses of 

 threads, whereas the non-conjugating threads are dark green, and 

 in open springy curves. The process can easily be followed. The 

 threads should not, however, be directly covered with the cover- 

 glass upon the object-slide, but the small pasteboard moist 

 chambers described upon p. 279 can be used with advantage, 

 the Spirogyra being placed in a drop suspended from the cover- 

 glass. If covered direct, pressure of the cover-glass should be 

 obviated by placing under its edges 

 narrow strips of paper. Conjuga- 

 tion in most cases takes place in 

 ladder-like fashion, i.e., two threads 

 lying alongside one another are con- 

 nected by cross bridges (Fig 107 A). 

 The cells put forth short blunt pro- 

 trusions, which come into contact, 

 and fuse with one another, forming 

 the conjugating canal. The cause 

 which brings about the formation of 

 these processes and their union is a 

 chemical stimulus. Curvatures can 

 also be induced by the same means, 

 by which threads not at first rightly 

 placed can assume the correct posi- 

 tion. In many cases we can dis- 

 tinguish prior to conjugation which 

 thread is male and which female, FIG. 107. Conjugation in spiro- 

 since the cells of this latter sex swell gyra ^ z > Zygospor 

 out into barrel-form ; but not infrequently this means of distinc- 

 tion is wanting. After the union of the conjugating processes the 

 contents of the male cell first round off, and finally withdraw on 

 all sides from the cell-wall. They then pass into the conjugating 

 canal, and through the middle partition walls, which in the mean- 



1 Fresh-water Algae can be obtained from T. Bolton, Balsall Heath Road, 

 Birmingham ; marine algse from the Biological Station, Plymouth. 



