1915] 



ATKINSON — PHYLOGENY IN THE ASCOMYCETES 



321 



under chemotactic stimulation, combined with a transverse 

 splitting of the oogonium or archicarp. 



The failure of the antheridium to perform its function 

 the sexual process, its reduction or loss, are well known fea 



tures 



the life history of a number of Ascomycetes 



In 



many cases where the antheridium or its supposed equivalent, 

 the spermatium, is to all appearance potentially functional, its 

 failure to function appears to be due to the sterilization of the 

 terminal portion of the archicarp. 1 



Analogous situations are known in the seed plants. I need 

 only cite the case of Elatostoma acuminatum (see Strasburger, 

 '09). The nucleus of the embryo sac mother cell enters the 

 preliminary phases of the heterotypic division. After synap- 

 sis the further stages of the heterotypic division are inhibited 



and by typ 



or 



get at 



division the eight-nucleated 



embryo sac is formed. The egg, therefore, ripens with a dip- 

 loid nucleus, and, without fertilization, develops the embryo. 

 The walls of the inner integument grow together at the micro- 

 pylar end of the ovule and harden, thus forming an effectual 

 barrier to the entrance of the pollen tube (Treub, '05; Stras- 



burg 



09) 



While great disturbances 



pollen de 



and most of the 



are em 



developed, some pollen is formed which appears normal. In 

 some cases the mother cell, which usually forms the diploid 



embry 



sac 



f 



ndergoes a true reduction division forming a 



row of four cells, the lower one of which forms a normal em 



bryo sac with a haploid 



The few m 



of this 



species, Strasburger thinks, result from fertilization of such 



1 While the "trichogyne" or terminal portion of the archicarp assumed vegeta- 

 tive characters in an increasing degree, it seems that it did not in every case 

 lose all of the features appropriate to a receptive organ. It appears in a few 

 cases at least to still respond to chemotactic or analogous stimuli, seeking the 

 fixed spermatia as in Collema pulposum (according to Bachmann, '13) and 

 Zodiomvccs vorticellarius (Thaxter, '96). In a number of cases there seem to 



triehogyn 



trichogy 



The perforation of the transverse 



trichogy 



appears to be another example of the retention of 



ancestral character of the 



m 



;gments 



genesis or apogamy was introduced. 



