HYBRIDISING AND CROSS-BREEDING. 



107 



of contrivances is actually found in nature for effecting this 

 end, which may be classified under the following heads : 



1. Protection by portions of the pistil or stamens themselves, 

 as in many Orchids, Aristolochias, Asclepiads, and the petaloid 

 stigmas of Iris. In the flowers of Lecythis (Monkey -pots), 

 part of the stamens are fused together into a unilateral cucul- 

 late body, which forms a roof or umbrella over the perfectly- 

 developed anthers and style (see Lindl., Veg. King., p. 739). 



2. By portions of the calyx and corolla; this occurs in an 

 immense variety of forms. 3. By sheaths, bracts, or foliage- 

 leaves. 4. By periodic movements of the leaves of the perianth, 

 as in the closing of flowers at night or in rainy weather. 5. 

 By curvature of the axis, as in those numerous flowers the 



An " echinated" or "spine-covered" 

 pollen - grain of a species of Tree 

 Mallow (Lavatera trimestris, L.), 

 mag. 200 times. 



Pollen of Clarkia elegans, Dougl. A, 

 Seen a dry object. B, Seen in -water ; a a' 

 The two layers of extine (inag. 200 times). 



opening of which is always turned towards the ground at the 

 period when fertilisation takes place. From the examples 

 adduced, Kerner draws the general conclusion that the protec- 

 tion of the pollen against the injurious effect of premature 

 moisture is the more perfect the smaller the number of flowers 

 and of pollen-grains in the individual, the greater their degree 

 of coherence, and the more exclusively the flower is fertilised 

 by insect agency. In those plants where the flowering extends 

 over a great space of time, where the anthers in the same 

 flower vary in the period of their dehiscence to allow the 

 escape of the pollen, and where the number of flowers in an 

 inflorescence is very large, the protection of the pollen against 

 the influence of the weather is reduced to a minimum, as in 



