2] THE VARIOUS GROUPS OF PLANTS 69 



one reaches the immediate proximity of the female gamete in the 

 ovule, there discharging the male gametes, one of which effects sexual 

 fusion. From the fertilized ovule the seed develops, contained in 

 the ovary which commonly becomes the fruit. Seeds and fruits, 

 though often alike in appearance, are technically very different and 

 should always be distinguished. Many fruits are attractive to 

 animals, or are winged or plumed to be caught in the wind, or 

 buoyant to float on water, being dispersed by these agents with the 

 seed inside. However, in those fruits which contain more than one 

 seed, it is more effective to liberate the seeds and have these individu- 

 ally attractive or appendaged for separate transportation. In any 

 case the embryo within, if still alive and given the right conditions, 

 germinates to form a new sporophyte plant which soon becomes 

 independent of any stored food-reserve and so completes the life- 

 cycle. Such is the general story — though there are all manner of 

 variations and even exceptions — in which it should be noted that 

 the gametophytes, both male and female, are microscopic, vestigial, 

 and entirely dependent on the sporophyte for food, the female being 

 so embedded therein that to all appearances there is only the one, 

 sporophyte generation. 



Asexual reproduction is extremely common and widespread in 

 Angiosperms. Not only are there numerous species which are 

 habitually parthenogenetic, the ovules developing successfully with- 

 out fertilization, but there is a wide array of vegetative means of 

 propagation in nature quite apart from those commonly practised 

 by Man. Familiar examples are the underground stems (rhizomes 

 and rootstocks) as well as suckers and overground runners and stolons 

 of many plants which, rooting at the nodes, constitute daughter 

 individuals on severance from or death of the parent. Also familiar 

 is the fragmentation of many water or colonial plants, as well as 

 separation of bulbs and tubers, while the production of bulbils or 

 young plantlets in place of flowers in many species, or in the axils 

 or even on the margins of leaves in others, affords further ready 

 means of vegetative propagation. Indeed, so common and effective 

 are these or other asexual methods, that many plants resort to them 

 habitually, and frequently are enabled by employing them to 

 reproduce and live indefinitely in regions where climatic or other 

 conditions prevent the ripening of fruit or even successful flowering. 



The mode of nutrition of most flowering plants is primarily by 

 their own photosynthetic activity, which takes place mainly in their 

 green leaves. Here, with the aid of chlorophyll in the light, they 



