FIG CULTURE 



of tree life and orchard management. Unless the 

 reader can assume that soil naturally contains suffi- 

 cient potash and phosphorus he is not ready to 

 study the more intricate subject of making natural 

 fertility available, nor to consider the more expen- 

 sive problem of maintaining adequate nitrogen, by 

 natural means, and artificial additions. The soil 

 is a storehouse of potash and phosphorus. This 

 broad statement is not literal, but punctuates the 

 fact that not only granite rocks and coarse sand, but 

 fine clays as well, are composed in part of these vege- 

 table foods. The roots do not push their tips into 

 such substances; they grow by tissue building like 

 coral reefs that rise from the bottom of oceans by 

 accumulations of one minute particle after another 

 upon the same foundations. They grow by ingest- 

 ing food in solution, and build tissues out of dilute 

 sap by chemical changes inside the trees. The tips 

 of root hairs absorb liquid through membranes; 

 hence we say that plant food must be brought to 

 the root terminals in the medium of water. Root- 

 lets digest the ingredients of former rocks, chang- 

 ing them into tissue and wood fibre, the terminals 

 proceeding between soil particles by a process of 

 accretion called osmosis. Like the building of an 

 icicle it continues along lines of least resistance. The 

 rootlets turn from lumps of clay, but grow rapidly 

 in decaying organic matter. If soil has become ce- 

 mented by rains, or baked in the sun, it is not con- 

 genial feeding ground. If trampled by stock while 



