BLAKESLEE. — SEXUAL REPRODUCTION IN THE MUCORINEAE. 289 



spores from the (4-) and (— ) strains. The zygophores which gave 

 rise to the progametes shown in Figure 40 a were observed, about an 

 hour before the drawings were commenced, to be in the same relative 

 position to each other as those figured in Figure 40 b. In both conjuga- 

 tions (a) and (b) the zygophoric hyphae met nearly terminally, while 

 the free hypha at (c) grew into contact with its complementary zygo- 

 phore from which three progametes had already been developed. In 

 Mucor V, a continuation of the growth of the zygophores after the first 

 contact is apparently the rule, and a consequent scalariform arrange- 

 ment of the zygospores very frequently occurs (Figure 44 b). 



The most noticeable vegetative difference between the (+) and (— ) 

 strains lies in the time of appearance of the sporangia. When tlie culture 

 photographed (Plate IV, Figure 53) was two days old, sporangia had 

 appeared in the growths from all the (+) inoculations, but even an ex- 

 amination under the low power of the microscope failed to show any 

 from the (— ) growths, and it was not until the day following that they 

 were observed. 



Mucor vi. 



The zygospores of this heterothallic species were first observed in 

 February last in a separation culture of a Mucor from a laboratory dung 

 culture, and the zygospores have been subsequently found on a later 

 spontaneous culture. 



Except in point of size, the individual zygospores resemble those of 

 M. Mucedo. The zygophoric hyphae are commonly branched, longer, 

 and less distinguishable from the sporangiophores. They are strongly 

 zygotactic, and the zygophores which developed in the region of contact 

 between the (+) strains in the culture photographed (Plate IV, Figure 

 54) showed from the centre of these neutral lines w'here the filaments 

 were uj)right, an increasing curvature toward the (— ) growth, separated 

 from them by the lines of young zygospores. 



The photograph fails to show the greater height of the (+) growth, 

 which is often distinctly noticeable under certain conditions, of cultiva- 

 tion, but the difference between the two strains is never so marked as 

 in the case of Mucor m. 



Summary of Heterothallic Forms. 



In the above nine species, which represent five distinct genera of the 

 Mucorineae, it has been shown that the formation of zygospores in all 

 cases results only through the interaction of two differing unisexual 

 mycelia which have been termed (-[-) and (— ). 



VOL. XL. — 19 



