71 INSECTS 
AND DISEASES 
That is why we add humus, why we fertilize, why 
we cultivate, and why we take note of our plants 
while growing. Only in this way can we supply 
their wants. 
Weeds spread diseases and we should be 
ashamed of them. Not only are they usually 
favorable to the growth of insects, scales and 
blights, but some kinds of weeds actually breed 
these parasites. Moreover, they rob the soil 
of nourishment during the dry, hot spells, thus 
bringing about various kinds of rots and mil- 
dews. And now it is supposed that they give 
out a kind of poison, or excrement, which ren- 
ders the soil unfit for crops. All this shows the 
necessity of clean cultivation if we would help 
our crops to resist both insects and diseases. 
