PLANT GROWTH WITHOUT FERTILIZERS 3 



amount of plant tissue is formed. It is from this carbon 

 dioxide that all the acids, carbo-hydrates, fats, proteins, etc., 

 are produced by the plant. In nature the concentration of 

 carbon dioxide in the air is not constant, but varies over a 

 wide range. The observations at Kew show extreme changes 

 of from 2*43 to 3^60 volumes of carbon dioxide per 10,000 

 volumes of air, with an average figure of 2*94. As is usually 

 the case in a set of statistics of this sort, the extreme figures 

 are very rare, and do not convey any very accurate mental 

 picture, but if we concentrate our attention on the month of 

 July, when active growth takes place, we find that in 1898 

 the amount of carbon dioxide was 2*83 volumes of carbon 

 dioxide in 10,000 volumes of air, whereas in the same month 

 of 1901 the corresponding figure was 3-11. It seems highly 

 probable that such a wide range would produce marked 

 influence upon plant growth, and consequently help to dis- 

 tort many of the smaller experimental investigations. 



Water Needed by Plants. A very large portion of any 

 plant is water. In the case of the seeds of most plants the 

 amount of water present lies between 5 % and 15 %, hay and 

 straw between 7 % and 18 %, grass from 50 % to 70 %, green 

 stuff, like cabbages, from 60 % to 80 %, and root crops, 

 such as potatoes, turnips, mangolds and beets, from 78 % to 

 92 % . Water is used by the plant for the process of transpira- 

 tion. On the average, one part of dry plant tissue, during 

 the process of its formation, necessitates the evaporation of 

 300 parts of water through the stomata of the leaves. Under 

 bad conditions of growth this figure can be very largely 

 increased, even perhaps up to 1000, but under good conditions 

 of growth, with a plentiful supply of plant food, such as 

 phosphates, nitrogen, and potash the amount can be markedly 

 reduced. 



Water plays a very important part in causing the 

 solution of many of the substances occurring in plant life. 

 Such materials as most of the common salts, like sodium 

 chloride, and some of the simple organic substances, like 

 sugar, belong to the group of crystaloids which dissolve 

 freely in water, giving a perfectly clear solution, passing 



