145 



The most frequent occurrence is dwarfing due to scarcity of water. 

 Like every other organism, the plant has the ability of adjusting itself with- 

 in wide limits to different conditions. An individual, accustomed from its 

 youth up, to a very scanty amount of water, can pull through with half the 

 amount of water used by a plant of the same species and variety, which had 

 developed with excessive water. Naturally the structure of the whole in- 

 dividual is adapted to these conditions. More thorough investigations have 

 been made with barley^, which was cultivated with a varied water content 

 in the soil (lO, 40, and 60 per cent, of the soil's capacity for absorbing water). 

 The most favorable water content for growth might be found possibly be- 

 tween 50 and 60 per cent, of saturation. 



In the experiment it was shown that the plant even with only 10 per 

 cent, of water had regulated its organization. Little leaf and root substance 

 had absolutely been formed, but the proportion between grain and straw 

 was normal; therefore about as much dry substance in the form of grain 

 as in the form of straw. With the same amount of food in the soil, the dry 

 substance increased as the roots obtained additional water. With too 

 much water, i. e., more than 60 per cent, saturation, very little dry substance 

 was produced absolutely and this small amount was worthless since the pro- 

 portion between straw and grain was changed, — to the detriment of the 

 latter. Measurement of the leaves showed that the grains grew longer and 

 wider, when water was supplied regularly and more abundantly. These 

 larger leaves, found with a greater water supply, are due partly to the in- 

 creased number of cells, partly to their greater distention. If the individual 

 cells of the upper epidermis are larger, it may be assumed from the ver}' 

 beginning, that the respiratory apparatus (the stomatal cells) will share in 

 the greater stretching of the upper epidermal cells and will also appear to be 

 the more widely separated thereby. Direct measurement confirmed this 

 assumption, so that therefore for each square centimetre of a leaf grown 

 with abundant water, fewer but larger stomata will be found,, than when 

 plants are growm with a scarcity of soil water. H. Moller has determined 

 by experiments- that plants dwarfed by lack of water (Nanism) are 

 structurally different from plants whose dwarfishness is due to a scarcity 

 of mineral substances in too weak solutions. In the latter the narrower 

 leaves are probably not due to narrower cells, resulting from water scarcity, 

 but to a smaller number of cells, since measurements show the same cell 

 breadth and the same size of the stomata in plants from a satisfactory nutri- 

 ent solution and from an insufficiently concentrated one. These differences 

 are easily explained. When the mineral substances are insufficient the cell 

 Increase will suffer only from water scarcity. The cells are less distended. 

 As shown by some of Moller's experiments with Bromus mollis, this nanism 

 is not hereditary, since specimens of huge size can be grown from the seed 



1 Sorauer, Einfluss der Wasserzufuhr auf die Ausbildung der Ger.stenpflanze. 

 Bot. Zeitung 1873, p. 145. 



- H. Moller, Beitrage zur Kenntnis der Verzwergung- (Nanismus), Landwirt- 

 schaftliche Jahrbiicher von Thiel., 1883, p. 167. 



