30 ALG^E 



Fertilization. Fertilization is accomplished when one of 

 the numerous male gametes swims to the female gamete and 

 fuses with it to form the zygote. The zygote by repeated 

 division develops at once into a many-celled embryo. This 

 early becomes differentiated into a holdfast and a growing 

 region which develops into a typical thallus. 



SUMMARY OF ALG.E. 



GREEN ALG! 



Plant. The plant of the simplest green alga consist of a 

 single cell as Protococcus, in others of a filament or chain of 

 cells as Spirogyra, in others of masses of cells assuming the 

 thalloid form as Choleochete. 



Reproduction. In Protococcus reproduction is asexual 

 since two plants are formed from one by cell division. Sex- 

 uality is shown in sphserella; the ciliated or motile zoospores 

 unite or conjugate to form a spore which produces a new 

 plant. In Ulothrix the spores are of different sizes and in 

 all cases a small spore unites with a large spore to form the 

 spore which develops the plant. In Spirogyra the contents of 

 a small cell passes into a large cell uniting with it to form a 

 zygospore or resting spore which after a time develops a new 

 plant. In Volvox the zygospore divides after resting into 

 four spores, each forming a filament. Differentiation of plant 

 structure and division of labor is shown in the Chseto- 

 phorales by the formation of a hold fast which serves to fix 

 the plant. In Vaucheria there are no cross-walls, the tubular 

 plant being multinucleated (ccenocyte), except during the 

 reproductive period; then cross-walls cut off the antheridia 

 or special male organ of reproduction. An antheridium con- 

 tains numerous sperms, and a hollow receptacle or archego- 



