88 PART I. THE MORPHOLOGY" OF PLANTS. [ 19, 20. 



ascocarp. In either case the result, is that a sporophyte is de- 

 veloped from that which either is, or represents, a gametophyte, 

 without the intervention of a sexual process. 



19. The Fruit. Although the forms of fruit occurring 

 among plants are so various in their form and in their structure, 

 it is possible to include them all in a single definition. A fruit is 

 the product of a process of growth initiated as a consequence of 

 a sexual act in structures which are not themselves immediately 

 concerned in the sexual act. 



To begin with instances among the lower plants, the cystocarp 

 of the Red Algae and the ascocarp of the Ascomycetous Fungi are 

 fruits. In these cases the effect of the fertilisation of the female 

 organ is not merely that the female organ gives rise to sporangia 

 (carposporangia in the one case, asci in the other) ; but the ad- 

 jacent vegetative tissues are stimulated to growth, forming an 

 investment to the structures developed directly from the fertilised 

 female organ, the whole constituting a fruit. 



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

 phyta, the effect of the fertilisation of the oosphere is riot 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 fertilisa- 

 tion 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 

 III., 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. 86). 



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

 Phanerogams, its morphology is discussed in connection with that 

 group (see Part III). 



