340 THE BIOLOGY OF FLOWERING PLANTS 



0.1, in the difference in growth rate between the " male " 

 aad " female " pollen tubes. In one species which shows 

 this, Rumex Acetosa, the male plants are markedly smaller 

 and less hardy than the females. The same is true of the 

 hemp. There is sometimes a marked difference between 

 male and female inflorescences, but differences between 

 pistillate and staminate flowers are scarce. The facts have 

 been collected by Goebel (1910 and Organographie), and 

 one or two examples may be given. In the maize the male 

 inflorescence is terminal and freely branched, the female is 

 lateral and simple. In Mercurialis perennis the female 

 inflorescences are short and have a few short-stalked flowers, 

 the male are longer with many sessile flowers. The orchid 

 Catasetum is a unique case ; the form of the perianth in 

 male, female, and hermaphrodite flowers is so different that 

 they were formerly referred to distinct genera ; the occa- 

 sional occurrence of two forms on one plant enabled them to 

 be identified. In our native Sagittaria sagittifolia the female 

 flowers are borne low down on the inflorescence, their 

 peduncles are twice as thick as those of the staminate flowers, 

 while the perianth of the latter is much larger. In most 

 cases it is impossible to assign a functional significance to 

 such differences. Goebel gives the case of Eriocaulon 

 nautiliforme y in which the pistillate flower has the posterior 

 perianth segment inflated to a bladder, which later acts as 

 a float for the fruit. 



§ 9. Pollination — The Stamens and the Pollen 



Pollination, the transference of pollen from stamen to 

 stigma, is the necessary preliminary to fertilisation and seed 

 production. The structure of the flower, especially in the 

 angiosperms, is intimately related to the accomplishment of 

 pollen transference. Except where reduction has taken 

 place the flower of the angiosperm possesses, in addition to 

 the " essential " organs, an envelope, the perianth, or two 

 envelopes, an outer calyx, typically protecting the flower in 

 the bud stage, and an inner corolla, typically bright and 



