igi2] SHARP— SPERMATOGENESIS IN EQUISETUM 97 



papillate cell as in the Filicales. The mode of development has 

 usually been correlated with the position of the antheridium 

 initial in the pro thallium. An adequate study of antheridium 

 development was not made in connection with the present work on 

 Equisetum arvense, but of the many young antheridia examined 



stakably of the latter form. Apparently any * 



unm 



prothallium 



able to divide periclinally and produce antheridia of the well known 

 imbedded type. 



chromatin 



form 



£> 



accumulated 



more 



asm 



conspicuous nucleoli are present. The cytop 

 cell generations may contain many plastids in various stages of 

 disorganization; in most cases these are no longer evident by the 

 time the 8 or 16-celled stage has been reached, but occasionally they 

 persist and are found in considerable numbers in the penultimate 

 cell generation, or even in the spermatids. It is obviously neces- 

 sary to select for critical study of the details of blepharoplast 

 development those antheridia in which the plastids' do not introduce 

 an element of uncertainty. 



The main point to be noted in connection with mitosis in the 

 early cell generations is that there are present no bodies which 

 could possibly be interpreted as centrosomes. The spindle libers 



without 



somes 



indication of approaching sperm 



is seen in the rounding off of the cells of the penultimate generation 

 (fig. 1). They begin to separate at the corners and gradually draw 

 away from each other until they are entirely free. Although the 

 division of these cells results in the production of sperms n pairs, 

 it becomes inaccurate to speak here of mother cells with two sperms 

 developing in each, since the intervening walls may persist until 



or may break down at once. By designating 

 them "penultimate cells" this ambiguity is avoided. Their 

 number at the time of rounding off varies greatly in different 

 antheridia. The observed range was 64 to 512, which means that 



the 



sperms are mature 



