CHAPTER I 



STRUCTURE AND PHYSIOLOGY OF THE PLANT 



LANTS EXERCISE TWO SETS OP FUNCTIONS — GROWTH AND REPRODUCTION. 

 The higher plants may be said to have three sets or classes of organs : those that have 

 relation with the soil ; those that have relation with the atmosphere and sunlight ; those 

 that are concerned in reproduction. For purposes of identification and description, and 

 to enable him to read current literature intelligently, the farmer needs some account 

 of these organs, and perhaps, also, 

 of some of the gross features of 

 the anatomy of the stem. 



Tlie external organs. 



The organs of the root series 



are the least differentiated. We do not 



distinguish plants by means of their root 

 characters, both because the roots are not 

 clearly designative in most cases and because 

 they are hidden. The most that we ordinarily do 

 is to divide roots into fibrous-form and tap-form. 

 The parts of the root are distinguished as to 

 their physiological functions rather than their 

 taxonomic or descriptive values. The general 

 form of the root is determined by the species ; 

 but its details are conditioned on the particular 

 soil in which it grows. It is often said of 

 orchard trees that the roots extend as far as the 

 branches of the top ; but the root system may be less or 

 more than the top in horizontal and vertical extent, depend- 

 ing on circumstances. Yet there is a distinct root " habit " 

 even as between varieties of apple trees. In the annual 

 crops, the root habit is often characteristic, and it needs 

 much more attention than it has yet received by cultiva- 

 tors (Fig. 4). The farmer may examine carefully the leaves 

 and stalks of his grass and wheat, but he seldom examines 

 the roots. Food for man and his animals is provided by 

 many thickened roots, as the greater part of the substance 

 of carrots, parsnips, turnips and beets. 



The stem, as named by the botanist, is the framework 

 on which the leaves and flowers are borne. The younger 

 growing parts of it, containing chlorophyll, may function 

 as foliage ; but the main ofiice of the stem is to provide 

 support. The stem may be very short and thick, as the 

 " crown " of turnips and beets, carrying the leaves ; it may 

 be exceedingly slender and light, as in the straw grains 

 and grasses ; or it may be high and massive as in the 

 trunks of trees. Sometimes the stem is subterranean, in 

 which case it is distinguished from roots by its buds or 

 "eyes," and rudimentary leaf -scales: the tuber of the Irish 



(5) 



Fig. 4. Comparison of root systems of barley 

 (above), and Indian com (below). (Minnesota 

 Experiment Station.) 



