334 ILLINOIS STATE HORTICULTURAL SOCIETY. 



almost ever)^, green thing, as well as most other life, would disappear 

 from that region as if by magic. 



The foregoing was written early in September last. Continued sub- 

 sequent observations, on leaf depredators, opened up an immense and 

 little known field of life. I found almost every species and variety of 

 plants having its leaves destroyed or greatly injured by some form of 

 life; the most prominent and destructive of these were acari ; but 

 fungi, aphides, leaf hoppers, bark hoppers, leaf folders, leaf rollers, leaf 

 crumplers, numerous species of Lepidopterous larvae, or caterpillar, and 

 other vegetable-feeding insects and larvae, assisted in the general destruc- 

 tion. The result of these observations left it no mystery why our trees 

 could not withstand a severe winter coming after a dry summer. The 

 wonder is how they can withstand any winter at all, be it severe or not. 



Leaves are, as is well known, as necessary and vital to plants as lungs 

 are to animals ; in fact their functions are greater than the lungs of ani- 

 mals, as they not only vitalize the crude sap or plant food, but elaborate 

 it also ; or, in other words, digest it. Weaken the leaves, and the whole 

 structure of the plant is weakened ; destroy them, and if the plant cannot 

 replace them, it is dead. Exactly in the same measure as the leaves are 

 injured, so is the whole plant weakened. If I have understood the office 

 of leaves rightly, their manner and times of performing their functions is 

 as follows : 



First. — As soon as they reach a certain maturity they elaborate ma- 

 terial for cellular, or woody fibre, that builds up the woody portions, as 

 the stems, twigs and bark. 



Second. — They elaborate material for the slightly differing cellular 

 tissue, or woody fibre of the roots ; and 



Third. — Toward the end of summer they elaborate these slightly 

 differing elements that are stored up in the cells of the wood, the roots, 

 the fruits (?) and the seeds, known as plant food, and on which, and the 

 quantity of them stored up, the future vitality and vigor of the tree or 

 seedling depends. According to this theory, if the leaves are weakened, 

 or interrupted early in the season, the tree makes but little growth of 

 wood ; if the same thing happens in the last half of summer, the roots are 

 weakened, and there is not a proper amount of plant food stored up in 

 the wood and roots of the tree. The roots may so lack their supply of 

 nourishment as to perish without the intervention of winter. Our grapes 

 refuse to ripen, and other fruits are astringent and unpalatable. In these 

 facts we have a full and true explanation of dead or weakened roots after 

 mild winters, as well as after severe ones ; which, experience has proved 

 to me, is often the case. 



The question of which are the greatest enemies to leaves, acan, fungi, 

 or leaf lice, is a hard one to settle. I am inclined in the belief that leaf 

 lice are ; not that their ravages are ever so great as those of the other two 

 sometimes are, but because I am loth to believe that fungi ever attack 

 healthy, living tissue, and from the well known fact that acari seldom, if 

 ever, injure healthy, normal life. The leaf lice first puncture, suck the 

 juices from, disorganize and weaken the leaf; these punctures form nidi, 



