FUNCTIONS OF THE FLOWER. 



39 



growth until it readies an ovule, penetrates this at a minute pore prepared 

 for its reception, and there deposits its contents (Figs. 77 and 78) ; ferti- 

 lization is then an accomplished fact, and the pollen and pollen-tube wither 

 away while the ovary and ovule continue their growth until the fruit is 

 matured. 



Even the most careless observer of plants must have noticed that in 



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n>. 



Fig. 7G.— Different forms of pollen. Magnified. 



many of our common species the fruit often contains abortive or imperfect 

 seeds. Pea-pods, for example, are often seen with only a single perfect 

 seed ; and ears of Indian corn with half the kernels imperfect are exceed, 

 ingly common. In these instances and in all others of like character the 

 ovules, represented by the imperfect seeds, have failed to be reached by 

 the fertilizing pollen-tube. Not unfrequently, also, dioecious plants, of 



Fig. 77.— Vertical section of an ovule before 

 fertilization. Magnified. 



Fig. 78.— Vertical section of an ovule after fertili- 

 zation, with pollen-Lube in situ. Magnified. 



the pistillate kind, and hence naturally fertile, bear flowers year after year 

 without producing fruit, much to the bewilderment of their owners. The 

 cause is not far to seek. Such plants are remote from individuals pro- 

 ducing staminate flowers, and must of necessity remain barren until this 

 fault be remedied. 



Another point of interest in this connection is the production of 

 hybrids, by the crossing of related species or varieties. 



