SPEEMAPHYTES : PHJENOGAMS. 



139 



nuclei of the spores, and very instructive preparations may thus be 

 made. 1 



The ripe pollen spores (Fig. 77, D) are oval cells provided with a double 

 wall, the outer one giving rise to two peculiar bladder-like appendages (z). 

 Like the microspores of the smaller club mosses, a small cell is cut off 



ar. 



in. 



FIG. 77. Scotch pine (except E and F}. A, end of a branch bearing a cluster 

 of male flowers (<3), x %. B, a similar branch, with two young female 

 flowers (?), natural size. C, a scale from a male flower, showing the two 

 sporangia (sp.), x 5. D, a single ripe pollen spore (microspore), showing the 

 vegetative cell (x), x 150. E, a similar scale, from a female flower of the 

 Austrian pine, seen from within, x 4. o, the sporangium (ovule). F, the 

 same, seen from the back, showing the scale (sc.) attached to the back. G, 

 longitudinal section through a full-grown ovule of the Scotch pine, p, a 

 pollen spore sending down its tube to the archegonia (ar.). sp. the prothal- 

 lium (endosperm) , filling up the embryo sac, x 10. //, the neck of the arche- 

 gonium, x 150. 



from the body of the spore (x). These pollen spores are carried by the 

 wind to the ovules, where they germinate. 



The wall of the ripe sporangium or pollen sac is composed of a single 

 layer of cells in most places, and these cells are provided with thickened 

 ridges which have to do with opening the pollen sac. 



See the last chapter for details. 



