450 NOtES AND MEMORANDA. 



capable of immediate germination, during which the central 

 vacuole becomes removed to the end towards the substratum, 

 whilst the green-coloured protoplasm becomes mainly col- 

 lected in the upper part, the colourless end tapering off in 

 order to penetrate the soil. A couple of weeks' continued 

 culture may again give vegetative plants capable of division 

 and of zoospore-formation. 



The isospores also present resting-stages, the form of the 

 originally globular cell becoming modified. Soon after con- 

 jugation these are flattened, with irregular lateral boundaries ; 

 these become on the following day exactly hexagonal. The 

 membrane of the isospore becomes thickened, and, on the 

 lateral margins, present some tuberculations, but there is 

 no secondary membrane formed. Brought upon damp earth 

 they soon become globular and otherwise behave as normal 

 isospores. In very young plantlets traces of the tubercula- 

 tions can be seen, but these soon disappear. The further 

 growth leads to the same result as that of the globular 

 isospores, that is, the formation of a vegetative plant. 



In order to distinguish that which appertains to the cycle 

 of alternation of generation from the remainder, the simple 

 way is to start from the fertilized germ (Ei) and see what 

 are the modifications of the plant, thence originating, actually 

 essential, in order to arrive again at the same reproductive 

 process. 



We have the isospore — it germinates — produces the 

 vegetative plant, which needs neither to divide nor to pro- 

 duce a sexual zoospore, nor to become an ordinary sporange 

 — it can directly produce spores. These close the first 

 sporophore generation. The second oophore generation 

 becomes presented in the germination Of these spores in the 

 form of sexual zoospores, which directly lead to the forma- 

 tion of the isospore — the limits of two generations. All 

 the rest are but phenomena of adaptation. 



Thus, in nature, the vegetative plants in spring almost all 

 become zoosporangia and spread the growth over considerable 

 areas. Zoospores which fall into water are not lost ; they ac- 

 quire a double membrane, and lie dormant until they chance 

 mechanically to arrive on moist soil. If drought sets in, the 

 plasma retreats to the roots. If the earth be some time a 

 little moist, the root-cells become hypnospores, awaiting 

 the rain in order to develope multitudes of zoospores. But 

 if the earth become rapidly dried the root-cells remain un- 

 unaltered until a moistening excites the formation of /oo- 

 spores. A great many of the root-cells can manifestly 

 accidontally reach the surface of the soil, and thus, according 



