4o6 THE BIOLOGY OF FLOWERING PLANTS 



vertically down. The position of the flower is related to 

 insect visits. Perhaps leverage is lessened by the position of 

 bud and fruit, the heavier fruit hanging down. In Erodium, 

 however, the bud is pendent and the fruit erect. 



Goebel (1920) holds that the pre- and post-floral move- 

 ments are related, based on the same mechanism, and 

 changing in direction with the changing metabolism of bud, 

 flower, and fruit. He does not think that, in most cases, 

 they have much biological significance. There is room for 

 experimental work on the subject. A detailed description 

 of many cases is given by Troll (1922). 



Post-floral Changes in Gymnosperms. — The post-floral 

 changes in the gymnosperms may be shortly referred to. 

 In most conifers there is considerable growth of the female 

 cone, both of the axis and of the sporophylls, and this is 

 followed by lignification and complete drying out. Move- 

 ments may be very conspicuous. The cones of Pinus 

 sylvestris are pendent when immature, erect at the pollination 

 stage, and again pendent as they ripen. In a few genera a 

 more or less fleshy " fruit " is formed. In Taxus the seed 

 is provided with a fleshy aril ; in Phyllocladus the ovule 

 becomes completely invested in an arillar outgrowth ; in 

 Podocarpus the sporophylls become fleshy and brightly 

 coloured ; the seeds of Juniperus are invested by the slightly 

 fleshy scales of the female cone. 



Induction of Post-floral Changes. — The statement that 

 the post-floral changes in the ovary and other parts of the 

 flower are the consequence of fertilisation is not always 

 correct. We have already seen that an embryo may develop 

 without fertilisation having occurred. Corresponding to this 

 parthenogenesis we have parthenocarpy , where a fruit is 

 produced without any seeds. This is the normal condition 

 in the cultivated banana and in seedless oranges, where the 

 fruit is the product of the ovary, and in the pineapple, where 

 the axis of the inflorescence and the bracts are concerned. 

 Where parthenogenetic seeds are produced, we might relate 

 the development of the fruit to the development of the seed, 

 but this cannot apply to parthenocarpic fruits. 



