220 PRACTICAL BOTANY 



made more apparent by plasmolysing some filaments with a 

 2 per cent, solution of common salt. 



2. The protoplasmic membrane, which lines the wall, and 

 incloses a large central vacuole which runs the whole length of 

 the filament : this membrane may also be more readily dis- 

 tinguished in plasmolysed specimens. In the membrane are 

 embedded 



3. Numerous oval, or spindle-shaped chlorophyll corpuscles : 

 look for some of these undergoing division. 



4. Round highly refractive oil globules, which are more or 

 less numerous according to the condition of the plant as regards 

 nutrition. 



III. On specimens which have been kept under conditions 

 favourable for strong growth, the sexual organs (gametangia) 

 are usually to be found in greater or less numbers. Having 

 found a specimen with mature sexual organs, examine first the 

 antheridium under a high power. 



1. The lower straight portion, or pedicel, rises vertically from 

 the main filament. 



2. The curved portion, or antheridium proper, differs from 

 the pedicel in the contents being for the most part colourless : 

 it is separated by a septum from the pedicel. When mature the 

 contained protoplasm forms a large number of small sperma- 

 tozoids, which escape through an opening at the apex. 



Next examine a mature oogonium in detail : note its sessile 

 position, and the septum which separates it from the main 

 filament : its oblique form and green-coloured, granular con- 

 tents : when actually mature an obliquely lateral beak is formed, 

 the apex of which becomes gelatinous, so that the motile sper- 

 matozoids can gain access to the ovum. 



IV. Observe the changes which succeed fertilization, re- 

 sulting in the formation of the ripe oospore : the chief are 



1. Formation of a firm wall completely surrounding the 

 fertilized ovum, and fitting closely within the wall of the 

 oogonium. 



2. An increase in the size and number of the oil globules : no 

 cell-division takes place. 



V. The reproduction by means of zoogonidia may readily be 



