6i6 



LECTURE XXII. 



cases the generative nucleus divides into two, and in some 

 cases a second nuclear division takes place. At the time of 

 fertilisation one of the nuclei thus produced escapes, together 

 with a certain amount of protoplasm, through the mucilaginous 

 apex of the pollen-tube. This gamete, as we may term it, 

 enters the female organ, makes its way to the oosphere, and 

 fertilises it. 



Fig. 70 (after Strasburger). Longitudinal section of the ovule of an Angiosperm 

 (Monotropa Hypopitys). m micropyle. syn synergidse. o oosphere. 



In the Cupressineae the mode of development is somewhat different, 

 since in these plants one pollen-tube serves for the fertilisation of several 

 female organs, and consequently several gametes have to be produced. 

 The first division of the generative nucleus in the pollen-tube of the 

 Cupressineee is followed by an aggregation of protoplasm round each of 

 the two new nuclei, so that two primordial cells are formed. Nucleus 

 division is repeated in the primordial cell which is the nearer to the apex 

 of the pollen-tube, without any corresponding cell-formation, so that 

 several nuclei are to be found in the dilated apex of the pollen-tube ; 

 these, with a certain amount of protoplasm, escape as gametes through 

 the mucilaginous apex of the pollen-tube, and each fertilises the oosphere 

 of an archegonium. 



