SECT. I. ACCESS OF THE POLLEN. 855 



female flowers stand close together, as in Typha, 

 Coix, Carex ; the females being lowest, and their 

 petals being deeply or minutely laciniated so as not 

 to interrupt the pollen in its fall, as in the genus 

 Pinns. 



The impregnation of Dioecious plants is often And dice- 

 effected by insects also, as has been already see 

 in the case of the Fig, and their flowers are said 

 to be always furnished with nectaries ; the male 

 flowers being larger than the female flowers, that the 

 insect, as it has been thought, may have the better 

 opportunity of loading itself with pollen.* 



From the fact of the agency of insects in con- 

 veying the pollen to the stigma it will follow that 

 no plant requiring such aid can possibly perfect its 

 seed unless the specific insect has access to it, or 

 unless some such aid is given to it by the cultivator. 

 And hence botanists attribute the imperfection of 

 the seeds of hot-house plants to the want of the 

 insect by which the species may be impregnated 

 in its native climate. This conjecture is counte- 

 nanced by the following experiment, as related by 

 Willdenow : A plant of Abroma august a had 

 flowered for many years in a hot-house at Berlin 

 without producing any fruit; but when the gardener 

 by means of a hair pencil placed a little of the 

 pollen upon the stigma of several of the flowers, 

 perfect fruit was produced from which new plants 

 were raised. 



* Willdenow, p. 3QQ. 

 2 A 2 



