VAUCHERIA 219 



SIPHONED 



VAUCHERIA SESSILIS, Vauch. 



I. This Alga is to be found growing as a lax green felt on the 

 surface of moist soil (frequently on the soil in pots in green- 

 houses) : it is of so coarse a texture that the separate filaments 

 can readily be recognized with the naked eye, having a some- 

 what dull-green, glassy appearance. Remove a small portion 

 of this felt : tease it out as gently as possible in water, and 

 examine it under a low power : observe 



1. The coarse, green, cylindrical tubes which constitute this 

 Alga. 



2. The absence of septa as a rule, though septa may be 

 present occasionally in unhealthy specimens, and are formed 

 in connexion with the reproductive processes. 



3. The very irregular monopodial branching. 



4. Some branches may develop as rhizoids, ramifying in the 

 soil, but these are frequently absent altogether. 



5. There may be present lateral outgrowths of peculiar form, 

 which are the organs of sexual reproduction (gametangia), 

 viz. 



a. Curved cylindrical bodies, which are the antheridia. 



b. Obliquely oval, sessile bodies which are the oogonia. 



In this species the sexual organs are associated together in 

 groups of two or three, each being inserted separately upon the 

 thallus : a single antheridium is usually associated with one or 

 two oogonia. 



II. Put on a high power, and examine the structure of the 

 thallus in detail. Note 



i. The smooth continuous external cell-wall: this may be 



