EFFECTS OF TRANSPIRATION. 



281 



750. The chief effects of transpiration upon the plant are: 

 (1) the transfer of dilute solutions of mineral matters to the 

 cells where assimilation, or the production of organic matter, 

 takes place ; (2) the concentration of these dilute solutions by 

 evaporation. The extent to which such concentration must 

 take place can be easily inferred from the large amounts of 

 water which are exhaled from some common plants under ordi- 

 nary conditions of culture. According to Haberlandt, 1 the total 

 amount of water exhaled from a plant of Indian corn during 

 173 days of growth was 14 kilograms ; of hemp during 140 days, 

 27 kilograms ; and of sunflower during the same period, 66 kilo- 

 grams. Hohnel 2 estimates the amount of aqueous vapor given 

 off between June 1st and December 1st, by a hectar of beech 

 forest (the trees averaging rather more than one hundred years 

 in age), to be between 2,400,000 and 3,500,000 kilograms. 

 That the leaves in autumn contain more ash constituents than 

 in spring, appears from numerous analyses, of which a few 

 are here given from Storer's compilation. 



751. Influence of transpiration upon the air. El >er mover 3 has 

 shown that in the course of the year the absolute humidity in the 



proportions of Labiatse, Liliaceae, Palmaceae, Myrtaceae, and Euphorbiacese ; but 

 the most characteristic orders are Zygophyllacese, Cactacese, Mesembryanthe- 

 macese, Cycadacese, and Proteacete (Constitution daiis le regne vegetal de 

 groupes physiologiques, Arch. Bibliotheque universelle, 1., 1874). 



1 Wissensch.-prakt. Untersuchungen, 1877, Bd. ii. , p. 158. 



2 Ueber die Transpirationsgrosse d. forstl. Holzgewachse, 1879, p. 42. Both 

 this and the preceding citation are from Pfeffer's Pflanzenphysiologie, i. p. 153. 



" Some of Haberlandt's figures for crops are obviously too high, probably 

 from overlooking the diminution in the rate of transpiration which attends 

 crowding plants together. Thus he makes the total amount of water exhaled 

 from an hectar of oats during the period of vegetation to be 2,277,760 kg. ; of 

 barley, 1,236,710 kg." 



8 Die physikalischen Einwirkungen des Waldes auf Luft und Boden, 1873, 

 p. 148. 



