REPRODUCTION 443 



into a special chamber inside the integument. Here it 

 puts out tubes, but the tissue of the ovule breaks down, 

 drawing the pollen grain close to the necks of the arche- 

 gonia. The cavity becomes filled with liquid, and the ciliated 

 gametes, when discharged from the germinating pollen-grain, 

 reach the female cells by swimming. The pollen chamber 

 receives the pollen in all the Gymnosperms, but in those 

 with nonciliated gametes the pollen tube acts as the carrier 

 of the gametes to the archegonia. 



In the Angiosperms one of the generative nuclei fuses 

 with the oosphere. In many families the other one has been 

 seen to fuse with the definitive nucleus. 



After the fertilisation of the oosphere in both cases an 

 embryo is developed from it, which remains enclosed in the 

 spore. In the Angiosperms fertilisation is followed not 

 only by the formation of an embryo, but also by a large 

 development of tissue arising in consequence of repeated 

 divisions of the definitive nucleus, so that the spore con- 

 tains a massive so-called endosperm in addition to the 

 embryo, the latter being usually embedded in the former. 

 This so-called endosperm has thus a different morpho- 

 logical value from the endosperm of the gymnospermous 

 plant. 



One of the most remarkable features about the struc- 

 ture and behaviour of the seed is the fact that soon after 

 the embryo is formed it enters upon a period of rest, which 

 in some cases is very prolonged. During this period the 

 seed becomes detached from the parent plant. The re- 

 sumption of its growth and development is known as the 

 germination of the seed. This resting period does not 

 occur during the development of the sporophyte in the 

 Cryptogams. 



The embryo frequently attains a considerable size before 

 its resting period commences. In this case it absorbs 

 the contents of the cells of a considerable part, or some- 

 times the whole, of the endosperm, so that it fills more or 

 less completely the cavity of the spore. 



