XXXIII REPRODUCTIVE ORGANS 455 



microsporangia in immense quantities, in the form of clouds 

 of light yellow powder called pollen. The microspore (b) 

 is at first an ordinary cell consisting of protoplasm with a 

 nucleus and a double cell-wall, but eventually the proto- 

 plasm divides into two cells ; a small one {a\ the vestige of 

 the male prothallus, which soon divides again forming two 

 or more cells, one of which is distinguished as the generative 

 cell ; and a large one {b\ the vegetative cell. Under favour- 

 able circumstances these cells undergo changes which will 

 be described presently. 



The structure of the female cone is best made out in the 



Fig. 1 20. — A single stamen or male sporophyll of the pine, showing 

 !he two microsporangia or pollen-sacs. 



larch. It also consists (Fig. 119, c) of an axis bearing 

 sporophylls {sp. ph. ? ), or, as they are usually called in 

 Phanerogams, carpels. Each carpel is a crimson leaf with a 

 green midrib produced distally into a projecting point, and 

 bears on its upper or distal surface a little flattened body, 

 the placental scale, on the upper surface of which are two 

 peculiarly modified megasporangia {ing. spg.), commonly 

 known as ovules. In the pine the placental scales (Fig. 121) 

 are larger than the carpels, and their thickened distal ends 

 form the rhomboid areas into which the surface of the cone 

 is divided, 



