FUNCTIONS OF THE FLOWEIJ. 



39 



r^rowtli until it reaches an ovule, penetrates tliis at a minute pore j^repared 

 for its reception, and there de^jOSits its conteutH (Fign. 77 and 78) ; I'erti- 

 Uzation is then an accoinplished fact, and the pollen and pollon-tubo wither 

 away -while the ovaiy and ovule continue their growth until the fruit is 

 matured. 



Even the most careless observer of plants must ' -/e noticed that in 



mm-.. 





Fig. 70.— DifTercnt forms of pollen. MnRiiiflod. 



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

 seeds. Pea-pods, for example, ai'o 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, r(>presented by the imperfect se(;ds, have failed to be reached by 

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



Fio. 77. — VertlcBl Bcction of an ovule before 

 fui'tilizntiim. M.i^nilieil. 



Flo. 7S. — Vortical Hec'ioii of an orule p.fter fortlH- 

 zatiun, wilh pollen-lube in situ. MngniHed. 



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 o* 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. 



