348 



PLANT MORPHOLOGY 



Male Gametophyte. The amount of vegetative tissue arising in the 

 male gametophyte varies according to the family. The most primitive 

 condition is seen in the Araucariaceae and Podocarpaceae, where two 

 prothallial cells are cut off, these soon dividing to form a tissue of many 



Fig. 298. Male gametophyte of Pinus nigra, X600. A, microspore; B, C, D, successive 

 stages in development of the pollen tube; E, pollen tube; p, prothallial cells; t, tube nucleus; 

 g, generative cell; s, stalk cell; b, body cell. (After Coulter and Chamberlain.) 



cells. In the Abietaceae two prothallial cells are formed but both of 

 them are ephemeral (Fig. 298A-C). Finally, in the Taxodiaceae, Cupres- 

 saceae, and Taxaceae, no prothallial cells are formed. The generative 

 and tube cells are nearly always differentiated before the pollen is shed 

 (Fig. 298Z)). All the conifers are wind-pollinated. In the Abietaceae, 

 with the exception of a few genera, e.g., Larix, Tsuga, and Pseudotsuga, 

 the pollen grains develop a pair of wings that grow out from the wall (Fig. 

 298). The Podocarpaceae (except Dacrydium) also have winged pollen 

 grains, but those of the other families are wingless. 



