40 VEGETABLE ORGANS. 



meshes of which are also situated spines (fig. 18) ; 

 and in the granules of chickweed the surface pre- 

 sents pits, with minute tubercles in the centre 

 (figs. 30 & 31). The pollen-granules are often con- 

 siderably altered by immersion in water; so that, 

 in judging of their structure when examined in 

 water, the resulting alteration must be taken into 

 account. 



When ripe pollen -granules have been immersed in 

 water for a short time, one or more minute tubes 

 will be seen protruding from their surface \ these are 

 the pollen-tubes, and the granular protoplasm con- 

 tained in them is called the fovilla. In the process of 

 fertilization of the flower, the pollen-granules fall 

 upon the viscid stigma ; the pollen-tubes are then 

 protruded, and, passing down the intercellular spaces 

 of the style (PL I. fig. 14), enter an aperture in the 

 ovule or young seed, which is thus endowed with the 

 power of growing into a new plant. The pollen- 

 tubes are often very long, and they do not exist fully 

 developed in the pollen-granules, but grow down the 

 style, just as the little rootlet of a seed grows into the 

 soil. The style of a crocus will serve for dissecting 

 out with mounted needles the long and very slender 

 pollen-tube (PL I. fig. 15). 



O'vary. The ovary by its growth and enlargement 

 becomes the fruit. There are many interesting mi- 

 croscopic structures to be found in fruits and the 

 seeds they contain, a few of which may be noticed 

 here. 



On examining the surface of the rind or pericarp 



epl, around, Kapiros, fruit) of an orange, little dots 

 will be seen, paler than the rest of the surface. These 

 are receptacles of secretion, or glands, containing the 

 evaporable or volatile oil upon which the fragrance of 

 the orange depends. They consist of loose cells, sur- 

 rounding a central cavity, and are imbedded in the 

 rind. 



