SEX IN LIVING FORMS 97 



an increase of heat, in some cases so marked as to be 

 readily detected with the thermometer. This is said 

 to be especially the case with the arum of Italy. 



In some plants in which the pistil is longer than 

 the stamens, thus elevating the stigma above the an- 

 thers, the female organ is often observed to bend over 

 and depress itself, so as to come within reach of the 

 anthers. 



In most instances, the fecundation of flowers is 

 chiefly effected through a purely mechanical process, 

 though in these cases, also, we see a wonderful adapta- 

 tion of parts to conditions. 



Natural Adaptations.— When the male and female 

 parts of flowers are situated on different plants, als in 

 the case of the willow, the poplar, the melon vine, and 

 many other species, the pollen of the male flower is 

 wafted by the wind or a gentle breeze to the stigma of 

 the female flower, which will usually be found at no very 

 great distance, although fertilization may take place 

 in this way at very considerable distances. Bees, moths, 

 and many other species of insects serve a very impor- 

 tant purpose in this work, transporting the fertilizing 

 dust upon their wings, antennae, sucking tubes and feet. 

 Small birds, and even the humble snail, which would 

 scarcely be credited with any useful function, are also 

 very serviceable in the same direction. The part per- 

 formed by insects in the reproductive process of many 

 plants is so great that they have been very poetically 

 termed "the marriage priests of flowers." 



Nature provides for thorough fecundation in these 

 cases, by placing the plants which bear the male and 

 the female flowers near each other. This fact accounts 

 for the unproductiveness of certain varieties of straw- 

 berries, unless mixed with plants of some other vari- 



