62 PART I. MORPHOLOGY. [ 19 



To begin with instances among the lower plants ; in most of the 

 Red Algse and Ascomycetous Fungi, the effect of the fertilisation 

 of the female organ is not merely that the female organ gives rise 

 to sporangia ; but the adjacent vegetative tissues are stimulated to 

 growth, forming an investment to the structures developed directly 

 from the fertilised female organ, the whole constituting a fruit, 

 known in the one case as a cystocarp, in the other as an ascocarp. 



Similarly, in the Bryophyta, and to a less extent in the Pterido- 

 phyta, the effect of the fertilisation of the oosphere is not merely to 

 cause the formation of an oospore and the development of an embryo, 

 but the wall of the archegonium is stimulated to fresh growth and 

 forms an investment, the calyptra, which encloses the embryo ; 

 sporophyte for a longer or shorter period, the whole constituting at 

 this stage a fruit. 



The most remarkable instances of fruit-formation are, however, to 

 be found in the Phanerogams. Here, as a result of the fertilisation 

 of the oosphere, various parts of the flower are stimulated to 

 growth ; most commonly it is only the macrosporophylls (carpels) 

 which are so affected, but the stimulating influence may extend to 

 the perianth-leaves or to the axis of the flower, the resulting tissues 

 being either hard and Woody, or soft and succulent (see Part IV., 

 under Phanerogams). The peculiar feature of the fruit of these 

 plants, as contrasted with those of the lower plants, is that here the 

 tissues affected all belong to the sporophyte, whereas in the lower 

 plants they belong to the gametophyte ; this is the necessary result 

 of the peculiar relation of the female gametophyte to the sporophyte 

 which obtains in the Phanerogams (see p. 3). 



19. The Seed. As this is a structure which is peculiar to 

 Phanerogams (p. 53), its morphology is discussed in connection with 

 that group (see Part IV.). 



