THE ALGAE 



95 



means of a branched holdfast or hapteron, which may be brown or white 

 in colour and is devoid of chloroplasts. The remainder of the coenocyte 

 contains a lining layer of protoplasm closely applied to the cell wall, and in it 

 are embedded numerous nuclei and chloroplasts. The central part of the 

 coenocvte consists of a vacuole containing cell sap. The chloroplasts are 



Zygote 



Microgomeles Macrogometes 



A- 



Male Female 



Cametangium Gometongium 



8ryops(s Plant 

 Fig. 76. — Life-cycle of Bryopsis. 



small and discoid, but in some species they become spherical when exposed 

 to intense light. 



In Vaiicheria the reserve material is oil, which is stored in countless tiny 

 droplets in the cvtoplasm. Under normal circumstances no starch is formed, 

 but under constant intense illumination it can be produced, which seems to 

 indicate that the appropriate enzymes are present. 



Injury to the thallus results in the formation of a septum sufficing to 

 isolate the injured part, but otherwise, with the exception of those formed in 

 relation to the sex organs, no septa occur. 



Asexual Reproduction 



Asexual reproduction takes place by the formation of zoospores (Fig. 77), 

 which are produced singly in club-shaped zoosporangia. The sporangia 

 develop singly from the swollen ends of the branches by the accumulation of 

 a large amount of cytoplasm with many nuclei and chloroplasts in the swollen 

 tip, which, as a result, diminishes the size of the central vacuole, and thus 

 these tips appear dark green in colour. Inside the zoosporangium a single 

 large mass is formed which is termed the zoospore. It contains many nuclei 

 which are arranged in a single layer near the surface and opposite each nucleus 

 a pair of flagella is developed. The zoospore is liberated by the breakdown 

 of the apical part of the wall of the sporangium to form a small pore through 



