PHYSIOLOGY -227 



The significance of the so-called india-rubber (CAOUTCHOUC) and GUTTA-PERCHA 

 in the latex in the economy of the plant is still less known. In addition to these 

 substances, there also occur in latex, resins, ethereal oils, alkaloids (in opium), 

 leptomin, starch grains, and other carbohydrates, oil-drops, and albuminous 

 substances. The presence of these substances valuable as constructive material, and 

 occasionally also of active enzymes (peptonising ferments are found in the milky 

 juice of Ficus Carica and Carica Papaya), in the latex, gave rise to the suggestion 

 that the latex cells and tubes function in the transport of the nutrient matter. 

 Our present knowledge of these often caustic and poisonous saps is limited to their 

 external utility in the economy of plant life. By their obnoxious properties they 

 defend plants from the attacks of enemies. Also, in the event of plants being 

 wounded, the latex is pressed out either by the surrounding turgescent tissue or by 

 the tension of the elastic walls of its own cells, and forms, as it quickly coagulates 

 in the air, an efficient covering for the wound. In other plants, especially in trees, 

 wound-gum serves the same purpose. (Pp. 134, 151.) 



Special Processes of Nutrition 



Parasites, Saprophytes, Symbionts, and Insectivorous Plants. 



The acquisition of organic nutritive substances through the activity of 

 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 assimilatory activity of green plants. Some plants 

 forego all attempts to develop an adequate chlorophyll apparatus, and 

 by so doing become unable 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 their 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 Bacteria and Fungi which nourish 

 themselves in this way as PARASITES (upon living organisms) or as 

 SAPROPHYTES (upon decaying remains of animals and plants and other 

 organic substances). 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 



