EFFECTS ON PLANTS 5 



yield energy. Growth ceases, but returns on refeeding. Hottes observed that 

 in developing beans, upon the removal of the cotyledons with their food supply, 

 the meristematic tissue which would normally produce the lateral roots is 

 transferred to the tip of the root and there used for growth. In 3 or 4 weeks 

 all the cells in the upper part of the root have lost most of their cytoplasm, and 

 the only actively functioning cells are those at the tip. Decrease in the size 

 of the root is due to decrease in the number of cells, rather than to decrease in 

 their size. Winkler ('13) also concluded that cell size is not greatly affected as 

 a rule by environmental factors, the size of a plant in general being due to the 

 number rather than to the size of the constituent cells. Maige ('23), however, 

 found a relation between the size of the nucleus and nucleolus and the amount 

 of nutrition in the bean seedling. 



The effects of inanition upon the growth and differentiation (as noted above 

 for sex) of plants also vary according to the age or stage of development of the 

 organism. Thus Davidson and Le Clerc ('18) found that the greatest increase 

 in the yield of wheat occurs when the soil fertilizer (sodium nitrate) is added 

 during the first stage of growth,' with a slighter effect in the second stage and 

 none in the third. Hoagland ('19) similarly noted that the yield of barley is 

 largely conditioned upon favorable supply and concentration of nutrients for the 

 plant during the first eight or ten weeks of the cycle. Urbain ('20) observed that 

 embryos deprived of their normal food (endosperm) at an early stage and placed 

 in nutrient solutions are inhibited in their later development, being dwarfed 

 and presenting various abnormalities (to be described later). 



Mode of Action. — Reed ('07) pointed out that the essential elements in 

 plant nutrition appear to act in two ways: (a) as component parts of the cell 

 structures or fluids; and (b) as indirect agents in causing less understood physi- 

 cal or chemical conditions necessary for the proper functioning of the cell, 

 whether as carriers of other ions, or as specific antidoting agents. Thus v. 

 Liebig ('76) found that ammonia stimulates plant growth, provided the other 

 necessary nutrients are present. Reed ('07) noted that algae thrive best in 

 neutral or slightly acid cultures, while phanerogams thrive best in neutral or 

 slightly alkaline solutions. Moore, Roaf, and Knowles ('08), in experiments on 

 the hyacinth and onion, found that alkalinity in general apparently stimulates 

 growth, producing increased nuclear division, changes in the chromosomes and 

 obscure cell-outlines; while acidity causes decrease or absence of nuclear division, 

 and thickening of cell-walls. Steinberg ('19) concluded that " Increased acidity 

 of the Pfeffer nutrient solution within a certain range results in the exhibition in 

 Aspergillus niger cultures of growth 'stimulation' like, but less in amount than, 

 that observed by addition of salts of certain heavy metals." The mode of 

 action in such cases is obscure and it is difficult to draw the line between growth 

 stimulants (including the vitamins) and nutrients. 



(B) Effects of Partial Inanition 



Heretofore we have been considering chiefly the effects of inanition in general 

 — of total inanition (excepting water), the nutriment being either entirely absent 

 (complete inanition) or reduced in amount (incomplete inanition). We have 



