438 VEGETABLE PHYSIOLOGY 



CHAPTEE XXVI 



REPRODUCTION (CONTINUED) 



WE have seen that the phenomena of fertilisation are 

 preceded in the Phanerogams by an arrangement through 

 which the two gametophytes which give rise respectively 

 to the male and female sexual cells are developed in such 

 close proximity that they ultimately come into contact. 

 That which is produced as the result of the germination 

 of the microspore or pollen grain, is a tube of varying 

 length, which bores its way through the tissue of certain 

 parts of the sporophyte, being guided in some manner not 

 yet fully understood, until it reaches some part, usually the 

 apex, of the megaspore or embryo-sac, in which synchron- 

 ously the prothallium which bears the oosphere has been 

 developed. In the process of sexual reproduction in these 

 plants we have two phenomena presented, which have 

 often been treated of as if they were inseparably connected. 

 The first of these, which is known as pollination, involves 

 merely the transport of the pollen grain to an appropriate 

 position on some part of the megasporophyll or of the 

 megasporangium itself. The second, which may or may 

 not follow the former one, is the actual fusion of the 

 gametes which are produced upon the gametophytes to 

 which the spores give rise, and which therefore must be 

 considerably later in the time of its occurrence. This is 

 what we have already described as fertilisation. 



It is necessary to insist on the distinction between 

 these two processes, as the phrase ' the fertilisation of the 

 flower ' is frequently somewhat loosely and erroneously 

 made use of when pollination is meant. 



We have seen that cross-fertilisation is as a rule more 



