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 in 

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

 tures in 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.^ 



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 typic or "vegetative" division the eight-nucleated 

 embryo sac is formed. The Qgg, 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- 

 burger, '09). While great disturbances occur in pollen de- 

 velopment and most of the pollen grains are empty or un- 

 developed, some pollen is formed which appears normal. In 

 some cases the mother cell, which usually forms the diploid 

 embryo sac, undergoes a true reduction division forming a 

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

 bryo sac with a haploid egg. The few male plants of this 

 species, Strasburger thinks, result from fertilization of such 



^ 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 

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

 be receptive areas on the trichogyne where the free sperms become fixed, where 

 fusion of sperm and trichogyne takes place. The perforation of the transverse 

 walls of the trichogyne, which is said to occur after fusion with the sperm, also 

 appears to be another example of the retention of an ancestral character of the 

 archicarp which primarily permitted the passage of sperm nuclei through the 

 terminal segment, or the association of nuclei of diflferent segments aa partheno- 

 genesis or apogamy was introduced. 



