SIPHONED. 



61 



aplanospores, and phytoamoebae (naked masses of protoplasm, 

 without cilia, which creep like an amoeba on a substratum) may 

 occur under certain conditions. 



The sexual reproductive organs are formed on short lateral 

 branches, and are separated from the vegetative cell (Fig. 58 A} by 

 cell-walls. Numerous spermatozoids, each with two cilia, are 

 developed in the coiled antheridium (A, ~b). The oogonium is a 

 thick, egg-shaped, often oblique cell, with its protoplasm rounded 

 into an oosphere, which has a hyaline " receptive-spot " (A, *) im- 

 mediately beneath the aperture formed in the wall of the oogonium. 

 A slimy mass, which serves to receive the spermatozoids, is formed 

 in some species in this aperture. The spermatozoids when liber- 

 ated swim towards and enter the oosphere, which then immedia- 



A 



FIG. 53. Vaucheria sessilis. 

 receptive spot. B Oospore. 



A Fertilisation ; b the antheridia ; a the oogonia ; a the 



tely surrounds itself with a thick cell-wall. The mature oospore 

 (B) contains a large quantity of oil. At germination the outer 

 cell-wall bursts and a new plant is formed. There is only one 

 genus, Vaucheria, with species living in salt as well as in fresh 

 water and on damp soil. 



Order 5. Phyllosiphonacese are parasites in the leaves and stalks of 

 Flowering-plants. 



Order 6. Caulerpacese. The thallus has distinct differentation 

 into root, stem and leaf-like members (Fig. 59) ; it is unicellular. 

 Within the cell, strong, branched threads of cellulose extend 

 from one side to the other serving as stays to support the 

 thallus. Reproduction takes place by detached portions of the 

 thallus ; no other modes of reproduction are known. This order 

 may most approximately be classed with the Bryopsidacece. The 

 genus Caulerpa consists of more than seventy species which 

 inhabit the tropical seas. 



Order 7. Codiaceae. The thallus has various forms, but with- 



