14 MANUAL OF BOTANY 



Even when the gametophytes are developed apart from the 

 sporophyte, the act of fertiUsation is often attended with the 

 same result. The body thus produced is known as the fruit. 

 In the latter cases the fruit is altogether a development of the 

 gametophyte ; in the former, the parts which form it are de- 

 rived from ths sporophyte, to which the gametophyte remains 

 attached. Thus in the flowering plants, the fruit is developed 

 usually from the central portion of the flower. 



The facts that the megaspore, or embryo sac, always remains 

 in the sporangium, or ovule, and that the gametophyte derived 

 from it never has an independent existence, lead to the produc- 

 tion of another structure, found at maturity usually within the 

 fruit, and known as the seed. When the gametophyte has been 

 developed it bears in the highest plants normally one sexual cell 

 or gamete, known as the oosphere. This is fertilised by the 

 male gamete while the whole gametophyte is still in the interior 

 of the sporangium, and the oospore resulting from such fertilisa- 

 tion germinates at once, starting the growth of the new sporo- 

 phyte. This growth takes place at first within the sporangium, 

 and proceeds for a longer or shorter period till the form of the 

 new sporophyte is clearly indicated in its parts. Then the 

 growth temporarily stops, and the sporangium with its contents 

 becomes separable from the sporophyte. The sporangium or 

 ovule has now become the seed, a structure which, from the 

 peculiarities of development indicated, is confined to the flower- 

 ing plants. It contains the new sporophyte, known as the 

 embryo, besides enclosing the remains of the gametophyte 

 which gave rise to the latter, and which may or may not con- 

 stitute the greater part of the structure. 



After the seed has been detached from the sporophyte it 

 remains quiescent for a variable time, but as soon as conditions 

 are favourable the temporaril3- suspended development is re- 

 sumed, and the new sporophyte soon attains an independent 

 existence. 



The formation of the seed is thus a special feature of those 

 plants in which the megaspore does not become detached from 

 the sporophyte, but develops in situ. This important peculiarity 

 marks off the large class of Phanerogams or flowering plants 

 from those below them in. the scale of development. In such 

 of the latter, known as the Cryptogams, as have megaspores 

 the latter are always detached from the sporophyte, and 

 therefore seeds are not produced. The gametophyte phase of 



