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^be pollen of tbe pine anb Bean : 



a Comparattpe Stut)^. 



By H. G. Wills, B.Sc, and A. H. Trow, B.Sc* 



THE mature pollen-grains of both Pine and Bean consist of 

 two nucleated cells — one known as the generative^ the other 

 as the vegetative cell. Both types of pollen-grain are micro- 

 spores. Regarded morphologically, the vegetative cell is con- 

 sidered to be a reduced prothallium, and the generative cell a 

 metamorphosised antheridium. The vegetative cell, from the 

 physiological point of view, must be regarded as a polar body. 



The two cells are enclosed in a common cell-wall, the outer 

 layer of which is strongly cuticularised. 



The chief differences between the two types may be exhibited 



thus : — 



Pine. Bean. 



I. — The pollen-grains possess lateral i. — The pollen-grains possess no 



vesicles or wings. lateral vesicles, but only small pro- 

 jections. 



2. — The vegetative cell is the small- 2. —The vegetative cell is the larger 



er and the generative cell the larger. and the generative cell the smaller. 



3. — There is a permanent wall be- 3.— The wall between the vegetative 



tween the vegetative and generative and generative cells soon disappears, 

 cells. 



Pollination is effected in the case of the Pine by means of the 

 wind ; in the case of the Bean by bees and other insects. 



In the Pine, at the time of pollination, the ovuliferous scales 

 separate. The pollen-grains, blown by the wind, fall on the upper 

 surfaces of these, and are guided by the projecting ribs of the 

 scales to the apices of the ovules. Hence, by a curving upwards 

 of prolongations of the integuments of the ovules, they are carried 

 to the micropyles. 



In the Bean, the stamens and stigma are so arranged that a 

 bee visiting the flowers to obtain food, carries away pollen-grains 

 from some stigmas to deposit them upon those of others. 



The wings or lateral vesicles of the pollen-grain of the Pine 

 increase its buoyancy, and so facilitate its dissemination. The 

 grains are dry, easily shaken out of the pollen-sacs, and produced 

 in enormous quantities. 



* From the "Intermediate Science Directory." 



