256 



BOTANY. 



from the former ; in other species the plants are dioecious, 

 and in them the antheridia produce motile spermatozoids, b} 

 means of which the fertilization is effected. After fertilization 

 each oosphere becomes covered with a wall of cellulose and 

 is thus transformed into an oospore. 



340. The development of the sexual organs of Achlya, 

 one of the genera of this order, is shown in Fig. 171, 6 to 

 10 ; at first there is a small pullulation upon the side of a 

 filament, as at 6 ; this soon extends into a bag-like projec- 

 tion (7), which is readily seen to be a young oogonium ; 

 it continues to enlarge, while its protoplasm becomes more 



dense, and at its narrower 

 part a second pullulation 

 forms (frequently two), as 

 shown at 8 ; when the larger 

 part has enlarged somewhat 

 more and become rounded, a 

 partition separates it from 

 the remainder of the filament, 

 and from the young anther- 

 idium, as shown at 9 ; the 

 protoplasm in the oogonium 

 forms several round masses 

 the oospheres and by this 

 time the terminal portion of 

 the antheridium is cut off by 

 a partition. In the monoe- 

 cious species a tube is formed by the closely applied anther- 

 idium, which penetrates into the oogonium through open- 

 ings in it formed by the absorption of portions of its wall 

 and comes in contact with one of the oospheres (Fig. 172). 



341. In some cases, instead of the oogonia developing 

 in the way described above, they are formed in the terminal 

 part of a filament by one or more partitions arising in it ; 

 such oogonia are cylindrical or barrel-shaped, and sometimes 

 several of them stand upon one another. The antheridia in 

 the species which have such oogonia are developed from 

 below the partition which cuts off the oogonium, and when 

 there are several superimposed oogonia it actually happens 



Fig. 172. Fertilization of the oospheres 



in Achlya racemosa. Each oogonium 

 contains two oospheres. Magnified. 



