GYMNOSPEEMS 



331 



as in the mandrake, although it resembles the sporophylls and 

 sporangia of the lycopods and cycads quite as closely as it does 

 the stamens of ordinary flowering plants. Each microsporangium 

 produces a large number of microspores by tetrad division of 

 microspore mother cells, exactly as in the ferns, Selaginella, and 

 cycads, so that the spore-forming processes in the spruce micro- 

 sporangia are identical with those of the sporangia of the lower 

 vascular plants already studied* The microspores of the spruce 

 are therefore true spores, exactly comparable to the microspores 



FIG. 195. Spruce twigs with staminate and ovulate strobili in May 



a s male strobili ; b, female strobili. Note the erect position of the female cones ready 



to receive pollen 



of Selaginella. Each microspore, or pollen grain, when mature, 

 is furnished with two expanded sacs, or wings (Fig. 198, c), 

 formed by the inflation of the outer coat of the microspore. When 

 the microspores are ripe, the microsporangia split down the center 

 of each sporangium, or anther sac, and the light-winged spores 

 are widely scattered, thus effecting pollination. 



The ovulate strobili grow at the ends of last year's twigs, 

 where they remain in the bud stage, like the staminate strobili, 

 through the first winter. They make their appearance, in tem- 

 perate regions, from the first to the fifteenth of May, occurring 

 as beautiful red erect strobili (Fig. 195, 5). They retain this 

 erect position for two or three weeks, until pollination is effected 



