106 HISTOLOGY AND PHYSIOLOGY. 



ASSIMILATION AND METASTASIS. 



135. The change into organic matter of the mineral or 

 inorganic substances taken into the plant as food is called 

 assimilation. The process takes place only in sunlight, 

 and then only in cells containing chlorophyll. It is, how- 

 ever, as yet but imperfectly understood. It appears that 

 water and carbonic dioxide become decomposed in the 

 chlorophyll-mass, and their elements recombined to form 

 carbo-hydrates. In most plants starch is the first visible 

 product of assimilation in the chlorophyll grains. Some- 

 times no ■ starch is formed, but instead, oily or sugary 

 matters, which are chemically similar. The oxygen in 

 starch is less than in water and carbonic dioxide, therefore 

 assimilation is a deoxidizing process, large quantities of 

 free oxygen being given off by the plant. Plants, destitute 

 of chlorophyll (as Indian-pipe, Beech-drops, Fungi, etc.), 

 are compelled to live on the assimilated products of other 

 plants, as in case of Parasites (Gr. para, beside ; sitein, to 

 feed), or on the juices or products of decaying organic 

 matter, as in case of Saprophytes (Gr. sapros, rotten ; phy- 

 ton, plant). 



136. Of the plants which obtain their food partly or 

 wholly from some other source than assimilation, there is, 

 besides the parasites and saprophytes, a group called 

 insectivorous plants. A common example is the Sun- 

 dew (Drosera), which grows in bogs and wet places. The 

 radical leaves are furnished witli stalked glands, whose 

 glistening secretion imprisons flies which alight thereon. 

 The flies soon die, and are then digested by the acidulous 

 secretion, which is at such time more copiously poured 

 forth. The nutritive portion is absorbed into the plant. 



