ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 401 



to meet the ovum, as plants became terrestrial and grew to 

 larger size. The distances to be traversed in order to accom- 

 plish fertilization became greater and the route lay through 

 the air; transportation became necessary; and it came 



about that the carriage of the 

 microspore, and not of the naked 

 sperm cell, was the plan that suc- 

 cessfully met the difficulties of 

 the situation. 



Flowering plants were sur- 

 rounded by various means of 

 transportation for their pollen. 

 Two of these were of prime im- 

 portance; the wind and winged 

 insects. The wind had certain 

 great advantages. It could be 

 be depended on to blow at all 

 seasons, night and day, and if 

 pollen were light enough, to sift 

 it everywhere, and to deposit 

 some of it in the right place for 

 cross fertilization. But on the 

 other hand, it was quite indis- 

 criminating as to where it should blow, and very wasteful 

 of pollen in consequence. Winged insects on their part, 

 having a liking for the nectar of flowers, would fly from 

 flower to flower with great precision, and if only the flower 

 could adjust itself to profit thereby, would distribute the 

 pollen with far less waste. But their aid was less trust- 

 worthy, and might at any time prove inadequate; they 

 were liable to casualties of storm and pestilence. Their 

 very power of selection might lead them to neglect one 

 species for others more attractive. And their aid was 

 most needed by species of sparse distribution. 



FIG. 235. Black oak flowers. 

 m, a single pistillate flower; n, 

 a single staminate flower, be- 

 fore the bursting of the anthers. 



