PHANEROGAMIA 



433 



The influence exerted by fertilisation is not restricted solely to the 

 formation of the seed. Other parts of the flower also undergo 

 modification and are adapted to new functions, such as the protection 

 and dissemination of the seeds ; while those parts which, after polli- 

 nation, are no longer of service, ultimately wither. 



The product of the changes induced by fertilisation in 

 the persistent parts of the flower is termed a fruit. the 

 formation of fruit, as well as the development of seeds, is an essential 

 characteristic of phanerogamic plants. Like the flower from which it 

 is produced, the fruit may also have a more or less complicated 

 structure. In the simplest cases it consists solely of the carpels 

 {e.g. Oruciferae), which, with the seeds, always constitute the essential 

 part of the fruit. Sometimes the flower-axis performs an important 

 part in the formation of the flower, particularly in perigynous and 

 epigynous flowers (e.g. Eose, Apple). Less frequently, the leaves of 

 the perianth are transformed into part of the fruit, as in Spinach, 

 when they form a hard, spinous envelope about the gynoecium. The 

 andrcecium, on the other hand, always disappears after pollination 

 has been accomplished. 



The once prevalent custom of considering the fertilised gyncecium alone as 

 the fruit is productive of great confusion. According to this view, only the 

 central portion of an Apple, for example, constitutes the fruit; while the larger, 

 peripheral portion, derived from the modified axis, would not he regarded as 

 belonging to it. The definition of a fruit given above is that adopted by Eichler. 



The seed, as a rule, falls to the ground, where, after a longer or 

 shorter interval, it changes from 

 its dormant state into an active 

 condition of life. This process 

 is termed germination. The 

 seed-coats are ruptured and the 

 embryo develops, without other 

 interruption than that occasioned 

 by climatic changes, into the 

 seed-producing plant (Fig. 364). 



General Classification. — 

 The Phanerogams are divided 

 into the two unequally large 

 classes, Gymnosperms and Angio- 

 sperms. The Gymnosperms are 

 the older class and occupied a 

 more important position in earlier 

 geological ages than at the pre- 

 sent time ; they now include 

 only a few hundred species. In accordance with their greater age, they 

 exhibit a closer alliance to the Pteridophytes than do the Angiosperms, 



2 G 



Fia. 364.— Thuja occidentalis. A, Seed in longi- 

 tudinal section ; c, cotyledons ; v, plumule ; h, 

 hypocotyl ; r, radicle : B-E, different stages of 

 germination. 



