THE VASCULAR CRYPTOGAMS 61 



III. THE OOPHYTE OR SEXUAL GENERATION 

 A. DEVELOPMENT AND STRUCTURE OF THE PROTHALLUS 



Fern spores can be sown successfully on ordinary 

 garden earth, on peat, on sand, or even on pieces of tile. 

 The last-mentioned material has the advantage that 

 very clean cultures can thus be obtained. It is well 

 to heat the soil, or whatever else is used, up to at least 

 100 C. (the boiling-point of water) before sowing the 

 spores, so as to destroy the germs of other organisms, 

 which are sure to be present, and which might compete 

 too successfully with the young prothalli. It is important 

 not to sow the spores too thickly, or else when they 

 germinate the prothalli overcrowd each other. The 

 cultures must, of course, be kept moist. It is best to 

 cover them with a bell glass, and to water from below. 



After about a week, the beginning of germination 

 may be observed ; the spore starts growing and bursts 

 its brown outer membrane. By this time the spores, 

 which in their resting condition are without chlorophyll, 

 will have begun to turn green. Fern spores which 

 contain no chlorophyll when ripe keep their power of 

 germination for a long time. In a few kinds, such as the 

 Royal Fern, Osmunda, the spores are green, and will only 

 germinate if sown at once. The first thing which the 

 germinating spore does is to form a root-hair. An out- 

 growth containing little or no chlorophyll arises from 

 the spore, becomes cut off by a cell-wall, and grows 

 down into the soil ; the remaining larger part of the 

 spore grows towards the light, and divides at first 

 transversely. A few more transverse walls are formed, 

 the end cell being always the one to divide, so that 



