The Plantlet. 43 
those belonging to the natural order to which the clover 
belongs (Leguminose (le-gu’-mi-no’-sz)) are able to appropri- 
ate nitrogen from the air (260). Phosphorus and sulfur 
assist in the formation of albuminous substances; potassium 
assists in assimilation (59); calcium and magnesium, while 
uniformly present, seem to be only incidentally useful. 
fron is essential to the formation of chlorophyll (58). Ex- 
cept the carbon and, in the case of leguminous plants, a 
part of the nitrogen, all these substances are obtained from 
the soil through the medium of the water absorbed by the 
root-hairs (101). 
Of all the materials obtained by plants from the soil, but - 
three, aside from water, viz., nitrogen, phosphorus and 
potassium (254) are needed in such quantities that the 
plants are likely to exhaust the supply, so long as water is 
not deficient. It thus appears that an adequate supply of 
water is the most important condition for the well-being of the 
plant, since it not only serves in nutrition, but is the vehicle 
by which all other food constituents, except carbon, are dis- 
tributed through the plant. The development of the plant, 
therefore, under natural conditions, depends very much 
upon its available water supply. Comparatively few soils 
are so poor as to be incapable of producing good crops when 
sufficiently supplied with water. On the other hand, the 
richest soils are unproductive when inadequately supplied 
with water. Much of the benefit of heavy manuring un- 
doubtedly comes from the increased capacity it gives the 
soil for holding and transmitting water. 
63. Water is Necessary to Growth. The supplying 
of food material is not the only office performed by water 
in the plant. The unfolding and expansion of the plantlet 
