sect, ii PHYSIOLOGY 207 



assimilating green cells is the most frequent, and is consequently con- 

 sidered the normal method of plant nutrition. Other modes of 

 nutrition are only possible at the cost of organic substances already 

 produced by the assimilating activity of green cells. The de- 

 pendent relations existing between the colourless and green cells, 

 and between the leaves and roots of all green plants, have already 

 been pointed out. Just as in the case of the cells devoid of 

 chlorophyll, some plants also forgo all attempts to develop an 

 adequate chlorophyll apparatus, and by so doing lose all ability to 

 provide themselves with nourishment from the inorganic matter about 

 them. 



Great numbers of such colourless plants derive their nourishment 

 from the bodies of dead animals and plants. All organic matter at 

 one time or another falls into the power of such plants as are devoid 

 of chlorophyll ; it is chiefly due to their decomposing activity in the 

 performance of the nutritive processes that the whole surface of the 

 earth is not covered with a thick deposit of the animal and plant 

 remains of the past thousands of years. These peculiar plants are not 

 satisfied with the possession of the lifeless matter alone ; they even 

 seize upon living organisms, both animal and vegetable, in their search 

 for food. 



It is chiefly the vast number of Fission-Fungi (Bacteria) and true 

 Fungi which nourish themselves in this way as PARASITES (upon living 

 organisms) or as saprophytes (upon decaying remains of animals and 

 plants). But even some species of the most widely separated families 

 of the higher phanerogamic plants have also adopted this method of 

 obtaining food. 



As a result of this modification of their manner of life, the organi- 

 sation and functions of these higher plants have undergone the 

 most remarkable transformation. From the corresponding changes in 

 their external appearance, it is evident how far-reaching is the 

 influence exercised by the chlorophyll. With the diminution or com- 

 plete disappearance of the chlorophyll, and consequent adoption of a 

 dependent mode of life, the development of large leaf surfaces, so 

 especially fitted for the work of assimilation, is discontinued. The 

 leaves shrink to insignificant scales, for with the loss of their assimi- 

 latory activity the exposure of larger surfaces to the light is no longer 

 essential for nutrition. For the same reason active transpiration 

 becomes unnecessary ; the xylem portion of the vascular bundle re- 

 mains weak, and secondary wood is feebly developed. In contrast to 

 these processes of reduction resulting from a cessation of assimilation, 

 there is the newly-developed power in the case of parasites to penetrate 

 other living organisms and to deprive them of their assimilated products. 

 In saprophytic plants, however, where the question is merely one of 

 absorbing nourishment from organic remains, the external adaptations 

 for taking up nourishment continue more like those for absorbing 



