THE AMERICAN BOTANIST 21 



the varieties of lettuce, cabbage, radish and other vegetables 

 produced by the gardener are regarded as not worth attention 

 from a true scientist. Nevertheless the only difference be- 

 tween the more recent species of the botanist and the new 

 "creations" of the gardener is that one is the product of 

 natural selection alone and the other of natural selection aided 

 by the art of the cultivator. One may be useless, the other 

 never is. In making this distinction between the useful and 

 useless, the species-maker is scarcely in an enviable position, 

 but it is doubtless far better for him to busy himself with use- 

 less things than to interfere in things of more value. 



Root Tubercles. — That practically all species of the 

 Leguminosae or pea family have small modules on their roots 

 inhabited by bacteria, is well known. These bacteria have 

 formed a sort of partnership with the higher plant and in ex- 

 change for certain plant foods which they receive, take the 

 free nitrogen out of the air and turn it over to their part- 

 ner. In this manner the legumes are able to grow in soils de- 

 ficient in nitrogen, and thus find a favorable habitat in regions 

 where other plants have difficulty in existing. While other 

 plants, so far as known, do not have the co-operation of these 

 helpful bacteria, many have arrangements "just as good." 

 For instance, a large number of our forest trees have myco- 

 rhiza on their roots. These are essentially fungus strands that 

 inhabit the outer layers of cells in the roots and act somewhat 

 after the manner of root hairs in other plants. A few other 

 plants develop "root-tubercles." These in appearance ^re 

 much like the nodules that appear on the roots of the legumes 

 only larger, and anyone who cares to see them may do so by 

 digging up the nearest plant of New Jersey tea (Ceanothus) . 

 These are inhabited by a fungus, which has the reputation of 

 getting nitrogen from the air like the clover bacteria and this 

 seems borne out by the fact that plants with these root tubercles 



