264 



STRUCTURE AND LITE HISTORIES 



After the zygote is formed, the outer wall thickens and 

 assumes certain external characteristics, easily recog- 

 nized. It also becomes black as it ripens, and this fact 

 has given rise to the common name, "black mold." In 

 this condition the zygote rests, as a zygospore. 



Fig. 190. — Sexual reaction between a hermaphroditic Mucor and (+) 

 and ( — ) races of a dioecious species. Diagrammatic representation of a 

 Petri dish culture showing a heterogamic hermaphroditic mucor (^) in 

 the center separated by channels on either side from the (+) and (— ) 

 races, respectively, of a dioecious species. Sp., sporangia containing 

 spores by means of which the plant may be reproduced nonsexually. 1-6, 

 stages in development of a hermaphroditic zygospore from unequal male 

 and female gametes. A, sexual reaction between a ( — ) filament and fe- 

 male gamete. B, sexual reaction between a ( +) filament and male gamete. 

 C, a male zygospore formed at stimulus of contact with a (+) filament. 

 (After Blakeslee.) 



256. Germination. — At the close of the resting period, 

 and under favorable conditions of temperature and mois- 

 ture, the zygote germinates, sending out an erect hypha, 

 which at once develops a globular sporangium at its apex. 

 The asexual spores from this sporangium become the 

 starting point of another series of changes like those 

 just described. 



256. Sexuality of Rhizopus. — It is well known that, 

 while conjugation often occurs freely between mycelia 

 from different spores, in other cases it fails entirely. The 

 explanation of this was not known until about eight years 



