GREEN ALGAE 



367 



divisions to form short discoid cells, which are the antheridia. Each, 

 on opening in the same way, sets free two spermatozoids, the result 



Fig. 271. 



Oedogonium. A = escaping zoospores. B=free zoospore. C -sexual organs 

 before fertilisation. D =in process of fertilisation. =oogonia ; a = dwarf-males. 

 S =spermatozoid. (After Pringsheim, from Strasburger.) ( x 350.) 



of division of its protoplast. They resemble the zoospores in form, 

 but are smaller. 



In some species special small plants (dwarf males) are produced from a 

 special type of swarmer known as an androspore, these being produced singly 

 within flat, discoid cells {androsporangia) which result from repeated trans- 

 verse division of the filament. The androspores attach themselves in the 

 neighbourhood of the oogonium, and dividing into a few cells, liberate their 

 spermatozoids close to the opening (Fig. 271, C, D). 



Fertilisation follows by fusion of the spermatozoid at the receptive 

 spot of the ovum, and the coalescence of the nuclei has been observed. 

 The zygote forms a firm protective wall : it is 

 stored with nutriment, takes a brown or red 

 colour, and may enter a period of rest. Its 

 germination presents a point of special interest. 

 The outer wall bursts and the contents escape, 

 contained within a delicate membrane. The 

 protoplast then divides usually into four cells, 

 which ultimately escape as motile zoospores 

 (Fig. 272). It has been ascertained in Oedo- 

 gonium capillare that the zygote nucleus under- 

 goes a reduction division : hence the Oedogonium 

 plant is typically haploid. Unfertilised oogonia 

 may occasionally germinate directly. In some 

 instances the zygote gives rise to a single large 



B.B. A 2 



Fig. 272. 



Bulbochaete intermedia. 



A = oospore. Z? = formation 

 of four zoospores in the 

 germinating oospore. (After 

 Pringsheim, from Strasbur- 

 ger.) ( x 250.) 



