6 INANITION AND MALNUTRITION 



now to consider the effects of partial inanition, only one or more of the essential 

 food factors being deficient. Aside from the carbon dioxide used for starch 

 formation in the green plants, the necessary factors include water and certain 

 mineral salts, especially nitrates and phosphates of calcium and potassium. 

 Magnesium, iron and sulphur also appear essential, at least in small amounts. 

 Some plants (fungi and many algae) require also organic (protein) nutri- 

 ment. The various factors are of unequal importance, however. Thus in the oat 

 plant, Dickson ('i8) found that a deficit of phosphorus or nitrogen is much more 

 injurious than a deficit of calcium, potassium or magnesium, which is in general 

 agreement with the earlier results of Reed ('07) in various plants. The effects 

 of the various substances upon plant morphogenesis and structure may be 

 designated as " Chemomorphoses " (Winkler). 



AQUEOUS INANITION (WATER DEFICIENCY) 



Water, as is well known, is a fundamental necessity for both plants and ani- 

 mals. Hygromorphosis is the primary factor in determining the form in many 

 plants, both higher and lower. With reduction of the normal supply of water, 

 many of the higher plants wilt through loss of turgescence due to osmotic pres- 

 sure. Sagot noted that dryness has a marked effect upon the structure of 

 plants. When growing plants are deprived of water, dwarfing and various 

 abnormalities of form may occur. Some amphibious plants have a water form 

 and a land form, apparently conditioned by the environment. 



Coulter, Barnes and Cowles ('11) classified plants, with reference to their 

 water requirements, as xerophytes, mesophytes and hydrophytes. "It would 

 seem that the chief determining factors of leaf size and proportion are those that 

 control the water supply." In the xerophytes (associated with water defi- 

 ciency), there is high transpiration through the leaves and low absorption of 

 water through the roots, resulting in leaves of small size and great thickness. 

 The thickness is due to a relatively large amount of cell-division in planes 

 parallel with the surface. They cite many variations experimentally produced 

 in the leaves and stems, the latter being shortened and thickened by dessication. 

 Upon the reproductive structures, dessication usually has an effect similar to 

 that of other unfavorable external conditions, frequently stimulating reproduc- 

 tion, but often inducing modifications of the normal process. 



Palladin ('18) likewise emphasized the marked differences in the dandelion 

 {Taraxacum officinale) and broom (Genistica anglica) grown in moist and in dry 

 air. "The difference is so great that they might be taken for distinct species." 

 As Palladin pointed out, however, water deficiency may arise in either of two 

 ways, diminished intake (through roots) or increased exit (transpiration through 

 leaves). The two modes may result in different morphological effects, as shown 

 by the experiments of Kohl ('86) on Tropaeolum majus (see accompanying 

 table). 



