142 Practical Plant Biology. 



is completed and its function discharged. It then turns brown 

 and withers. Taking its origin from the gametes of the leafy 

 moss-plant it has developed into an organism wholly unlike its 

 parent It is evidently the asexual spore-producing phase the 

 sporophyte succeeding the sexual phase the gametophyte and 

 we have to do with an alternation of generations quite similar to 

 that occurring in Marchantia and probably comparable to that 

 found in Polysiphonia. The two phases are relatively simply 

 organised and equally developed in Polysiphonia, while in Mar- 

 chantia the sporophyte generation is inconspicuous compared to 

 the large green complicated thallus of the gametophyte. In 

 Funaria we have the two generations fairly equalised in size and 

 complexity 'of structure. In Polysiphonia the two generations are 

 independent of each other from the germination of the reproduc- 

 tive body which gives origin to each of them. This is not the 

 case with Marchantia. There the germinating spore gives rise to 

 the physiologically independent holophytic gametophyte. The 

 generation developing from the oosperm obtains all its substance 

 and nutriment from the tissues of the supporting gametophyte. 

 It never makes attachment with the earth to obtain a supply of 

 the nitrates and other mineral salts absorbed by holophytic plants ; 

 it possesses no photosynthetic organs or tissues, whereby it might 

 manufacture carbohydrates from carbon dioxide and water. It 

 develops wholly parasitically on the gametophyte, at first wholly 

 enclosed in it, and only breaking forth from its surface when 

 development is complete and it becomes necessary to shed the 

 spores. 



In Funaria, during the early stages of development, the sporo- 

 phyte is entirely parasitic upon the gametophyte. Through the 

 foot it absorbs all its requirements from the tissues at the base of 

 the archegonium, organic substances-, mineral solutions and water. 

 As it develops, chloroplasts are formed in its superficial cells and 

 no doubt supplement the organic substances transmitted from the 

 gametophyte, by carbohydrates produced in situ by photosynthesis. 

 Tissue specially differentiated for this function is developed round 

 the conducting strand in the base of the theca and forms the 

 apophysis. 



The cells forming the outer layers of the apophysis are thin 

 walled and contain large numbers of chloroplasts, and the carbon 

 dioxide of the air is conveyed to their surfaces by intercellular 

 passages which extend inwards among the cells from the surface. 

 Lest these intercellular passages should, by permitting too free an 

 escape of water vapour, allow the drying up of the photosynthetic 



