350 Conjugate 



One of the conjugating cells is thus completely emptied while the other 

 lodges the zygospore (fig. 218 C). The gametes may coalesce immediately on 

 contact or for a brief period they may lie side by side in the gametangium 

 before fusing. 



The fully-formed zygospore is generally ellipsoidal, but it may be spherical, 

 and sometimes it is distinctly compressed, as in Spirogyra maxima, Sp. majas- 

 cula and others. It provides itself with a thick wall of three coats (vide De 

 Bary, '58, and others). The outer coat consists mostly of cellulose and is the 

 first-formed wall of the zygospore. The middle coat, which is generally 

 stronger and thicker, gives no cellulose reaction, and is apparently partially 

 chitinized. It is usually of a brown colour, and in many cases is furnished 

 with small, irregular and anastomosing ridges, or with scrobiculations. The 

 inner coat is the most delicate and consists of pure cellulose. 



The fusion of the nuclei is delayed for some time after the formation of the zygospore. 

 Overton ('88) and Klebahn ('88) each stated that the fusion did not take place for weeks 

 or even months after the complete formation of the zygospore, l>ut Chmielewski ('90) 

 declared that fusion occurred quite soon after the union of the gametes, and that it was 

 followed by two successive mitotic divisions resulting in four nuclei. Two of these decay, 

 the other two uniting to form the 'secondary nucleus' of the zygospore 1 . Trondle ('07) 

 states that the nuclei of the gametes lie side by side for about seventeen to twenty-one 

 days, and then fuse. He confirms Chiuielewski's observations on the double mitotic 

 division with the formation of four nuclei and the subsequent fusion of two of them. The 

 whole process is, however, at present rather obscure. Karsten ('09) has also observed the 

 double mitosis of the zygote-nucleus and states that the first division is heterotypic. 



Concerning the behaviour of the chloroplasts of Spirogyra during conju- 

 gation there is much difference of opinion. Overton ('88) stated that the 

 chloroplasts of the two gametes disorganized and became amalgamated, whereas 

 Chmielewski ('91) states that only the chloroplast of the male gamete dis- 

 organizes, that of the female gamete remaining intact. There appears to be 

 good evidence that in some species both chloroplasts disintegrate during 

 conjugation, and it may be that the behaviour of the chloroplasts during 

 conjugation is not precisely uniform. In Sirogonium the chloroplasts of 

 both gametes disintegrate at the very commencement of conjugation. 



The mature zygospores are usually brown or sometimes brownish-red 

 in colour, and most of the starchy reserves are usually converted into a 

 fatty oil. 



On the germination of the zygospore much starch appears and the oil 

 vanishes. The two outer coats are ruptured, generally at one end of the 

 spore, and the inner coat is protruded as a short outgrowth. Nuclear- and 

 cell-division soon occur and the outgrowth becomes divided by a transverse 

 wall (fig. 218 G), one cell sometimes developing organs of attachment and 



1 Compare with Kurssanow's statement concerning Zygnema (vide p. 344) 



