292 XXII. REPRODUCTION OF ALG^E. 



time had become softened. The female cell had either rounded 

 simultaneously, or rounds off on entrance of the male cell. Both 

 cells come into contact, and after a few minutes coalesce. Their 

 contents blend. The zygote or zygospore thus formed begins 

 at once to contract ; after the course of an hour its vacuole, 

 hitherto filled with cell- sap, has completely disappeared, the cell- 

 sap being expelled. The vacuole is again formed about twenty- 

 four hours later. A membrane with clear double contour then 

 clothes the zygote (Fig. 107 A). 



Thus much can be seen without reagents. If, however, the 

 object is fixed and stained during conjugation, say with 1 per 

 cent, osrnic acid, and made transparent by placing in dilute glycer- 

 ine, which is allowed gradually to concentrate by evaporation of 

 the water, it can be determined that the two nuclei of the con- 

 jugating cells, after the fusion of these latter, gradually approxi- 

 mate and ultimately combine into a single one. The whole of 

 one thread is emptied, the other contains zygospores ; the former 

 is male, the latter female ; that is, the threads are unisexual. 

 Of the chlorophyll bands only that (or those) of the female cell 

 remains intact ; that of the male falls to pieces, which more or 

 less completely disappear. The ripe zygospore acquires ulti- 

 mately a thick membrane, in which several layers can be dis- 

 tinguished, of which the outermost and innermost are colourless, 

 the median is brown. In the interior of the zygospore numerous 

 oil-drops are produced, and flecks of a red or reddish- brown 

 pigment. Occasionally the cells of a thread may conjugate 

 with either of two other threads ; and in other cases two 

 adjoining cells of the same thread may coalesce by a curved 

 conjugating canal (Fig. 107 B) showing that threads can be 

 monoecious, 



Spirogyra which one has in cultivation (see p. 251) can be very 

 readily induced to conjugate at any time between mid-February 

 and the beginning of May, by placing it in 2 per cent, to 4 per 

 cent, solution of cane sugar and in a sunny position ; and the 

 same end can be attained with plants in the sun, but in a very 

 small quantity of water. If the alga has, naturally, a predis- 

 position towards conjugation, this can be brought about upon the 

 micro-slide in J per cent. Agar-agar jelly. As the threads 

 cannot change their position in this, only those threads which 

 lie suitably towards one another can put out their conjugating 

 processes. The other cells must remain sterile, but after some 



