104 PART I. ORGANOGRAPHY. 



equally remarkable changes take place in the character and con- 

 sistence of its walls. Compare, for instance, the ovary of the 

 apple in flower with the ripened fruit, or the pistil of the cherry 

 blossom with a ripened cherry. Moreover, organs exterior to 

 the ovary feel the influence of the process. Even pollination is 

 sufficient, in many cases, to cause the stamens and corolla to 

 wither and fall away before the pollen-tubes have had time to 

 reach the ovules. It is well known that the period of blossoming 

 may be greatly prolonged in most flowers, if the pollen be pre- 

 vented from gaining access to the stigmas. The results of the 

 fertilization also often affect organs as far removed from the 

 ovule as the calyx and receptacle, and even the bracts beneath 

 the flower. Indeed, the influence is even more far-reaching than 

 this, for the enormous development which the fertilized pistil 

 undergoes, shows that all the nutritive processes in the plant 

 must be more or less deeply affected. 



Practical Exercises. 



i. Compare the flowers of the Plantain, Indian Corn, Wheat, Timothy 

 Grass and Hazel, all of them anemophilous, with the flowers of the Geranium, 

 Pink, Apple, Buttercup, Poppy, or other entomophilous flowers, and note (i) the 

 difference between the stigmas of the two groups as regards the extent of sur- 

 face which they expose ; (2) the difference as to the abundance and character 

 of the pollen ; (3) the difference in showiness, presence or absence of perfume, 

 etc. (4) Observe in the Geranium whether the flower is proterandrous, proter- 

 ogynous, or whether the maturing of the stigmas and anthers is simultaneous. 

 {5) Observe different flowers of the Pink, and note the difference between the 

 staminate and pistillate stages. (6) Ascertain whether the anthers of the But- 

 tercup dehisce extrorsely or introrsely, and state, if you can, what relation the 

 facts you discover bear to the cross-fertilization of the plant. 



2. Examine the flowers of the common Blue Flag ; note the position of 

 the nectar, the relative position of the anthers and stigmas, which way the 

 anthers face, and the mode of their dehiscence, and determine, if you can, the 

 manner in which cross-fertilization is effected. 



4. Examine the flowers of the common Barberry ; observe the relative 

 arrangement of the stamens and petals ; observe the structure of the anthers, 

 and their mode of dehiscence ; by means of a pin irritate them slightly at the 

 base, and observe the movement ; note the shape of the stigma, and the position 

 of the nectar secretion ; if possible, observe the flower while it is being visited 

 by an insect, and then explain its adaptations to cross-fertilization. 



Other interesting flowers to study for the same purpose are those of the 

 Milkweed, the Cypripedium, the Pea, and the common Mallow. 



