THE ALG^E 



187 



s p: 



The plurilocular sporangia, unlike those just described, 

 are multicellular structures. In this case the sporangium 

 is divided up by numerous cell-walls, usually longitudinal 

 as well as transverse, into a multitude of small compart- 

 ments (see Figs. 78 and 80). In each of these com- 

 partments one or two zoospores are formed, which do not 

 differ obviously from those arising in the unilocular 

 organ. The zoospores escape from 

 the plurilocular sporangium by a 

 single opening at the end, the walls 

 between the different compartments 

 being absorbed, so that the swarming 

 cells can pass out, one after another, 

 through the same aperture. 



In a very few cases (one of which 

 is illustrated in Fig. 80), the swarm- 

 cells from plurilocular sporangia 

 have been observed to conjugate. 

 In Ectocarpus siliculosus there seems 

 to be a certain functional difference 

 between the sexes, though in appear- 

 ance the conjugating cells are all 

 alike. Certain of the swarming 

 cells (planogametse) come to rest 

 before the others, and withdraw their 

 cilia. Such a cell, which we may 

 regard as female, exercises a remark- 

 able attraction on the others which are still swim- 

 ming about. They swarm round it in great numbers 

 (as shown in Fig. 80, B), and eventually one of the 

 8 warmers begins to fuse with the res ting-cell. The two 

 are at first connected by means of one of the cilia of the 

 active cell. This cilium gradually contracts, and the 



FIG. 79. Unilocular 

 sporangia (sp) borne 

 laterally on a filament 

 of Ectocarpus ovatus. 

 Magnified 300. (After 

 Eeinke.) 



