BLAKESLEE. — SEXUAL REPRODUCTION IN THE MUCORINEAE. 275 



ami fiirtluT function merely as tubes for the transmission, by way of the 

 suspensors, of nourishment used in tiie formation of the zygospores. 



As has been ah-eady mentioned in the Introduction, the account 

 current in text-books states that cUih-shaped outgrowths (jirogametes) 

 arise from adjacent sides of hyphae not ah-eady in contact and by mutual 

 attraction come to meet at their swollen extremities. In no form which 

 the writer has under cultivation have the gametes been found to be cut 

 off from portions of the zygophoric hyphae which were present before 

 they became approximated. It is only from those structures (progam- 

 etes), which have developed from the zygophores as a result of their 

 contact, that gametes are delimited. The condition has been correctly 

 interpreted by Falck ('01) from an observation of j'oung stages, and the 

 erroneous opinion just referred to is no doubt due to the difficulty usually 

 associated with any attempt to follow the process by direct observation. 

 Investigators have in general been dependent on a comparison of young 

 stages as a means of reconstructing the process, and have regarded as 

 typical the abnormal conditions frequently encountered in which the 

 apposed progametes have either been torn apart in the dissection of the 

 preparation examined, or, in cases where the zygospores are arranged in 

 a scalariform fashion, have been separated by the more rapid development 

 of a zygosj^ore between the same hyphae. 



After the progametes have attained a considerable size there are 

 formed in turn, generally not at the same time, septa which cut off more 

 or less equal terminal cells — the gametes (Figure 29a) — and by the 

 subsequent dissolution of the intervening wall, which proceeds from the 

 centre outwards (Figure 34), an open communication between the con- 

 tents of the two cells is afforded. The zygote thus formed by an increase 

 in size, a rounding out of its contour, a darkening and denticulation of 

 its outer wall and the formation of a thick layered hyaline one within, 

 assumes the character of the mature zygospore (Figure 35). 



In the main the description just given will probably apply equally 

 well to the majority of the heterothallic forms. 31. Mucedo is peculiar, 

 however, in that its zygophores are sharply differentiated from the spor- 

 angiophores and rarely if ever bear sporangia. They are seldom even 

 branched, and a scalariform arrangement of the zygospores, which is 

 characteristic of certain members of the genus Mucor, has never been 

 observed. 



The stages in the process of conjugation may be illustrated by the 

 series shown on Plate II, Figures 2o to 32, which consist of camera 

 drawings taken at the intervals noted from a Petri dish culture iu the 



