Letters on the Diseases of Flants. 39 



In the United States the plants that have been found to be attacked by 

 Tylenchus arenarms of Neal, which is the same as the Australian worm, are 

 as follows : — 



Badly affected. — Eoots of cabbage, kale, potato, banana, radish, okra, pea, 

 peanut, cow-pea, bean, squash, pumpkin, melon, cucumber, tomato, beet, 

 plum, apricot, peach, almond, fig, English walnut, willow, gourd, bigonia, 

 sunflower, amaranth, dahlia, koniga, iberis, coleus, achyranthes, purslane, 

 sand-purslane, verbesina, worm-wood, Jerusalem-oak. 



Slightly affected. — Roots of cotton, egg-plant, pepper, spinach, cassava, 

 maize, orange, grape, mulberry, walnut, pecan, hibiscus, ice-plant, parlor ivy, 

 morning-glory, nolana, petunia, boussingaultia, spirea, flowering almond, 

 buddleia, cape jessamine, shepherd's purse, blackberry, dewberry, eupatorium, 

 cypress vine. 



These lists include the majority of the most useful food-plants, many 

 ornamental plants, and a number of the commonest weeds. Among the latter, 

 the roots of purslane, amaranth, Jerusalem-oak, and worm-wood harbour the 

 greatest number of worms. 



The extent of the damage done by gall- worms is difficult to estimate. 

 Much land in Europe has become so badly infested that certain crops — for 

 example, sugar-beet — have had to be abandoned altogether. Not a beet-root 

 will mature. The plants break the ground, languish a few weeks, and then 

 die. Since time immemorial, crops of various kinds have died suddenly — 

 so suddenly, Dr. Neal remarks, as to justify the expression, " struck by 

 lightning." The unknown cause in some such cases has probably been the 

 gall-worm. Many an agricultural or horticultural failure attributed to the 

 use of improper fertiliser, to poor soil, or wrong cultivation, has been due to 

 this insidious foe attacking the very fountain-head of vegetation. Were it 

 possible to sum up in pounds, shillings, and pence the damage done by 

 gall-worms, the total would probably amount to a fortune for a nation. 



Remedies. 



All that can be done in combating root-gall must be directed toward 

 prevention. Once the gall-worm gains access to the roots, the game is up. 

 A leaf-destroying pest may be dealt with even after its attack has made some 

 progress, but thus far, at least, roots and rootlets are largely inaccessible 

 except at the expense of the life of the plant. Hence it follows that all 

 rational remedies for root-gall must be directed either toward ridding the soil 

 of the gall-worms, or toward putting such obstacles in their way, or so 

 reducing their number, as to render their ravages bearable. These ends have 

 been sought in various ways. 



1. By the use of some chemical, preferably a fertilizer, which will 



destroy the free-living larvae. 



2. By the selection of varieties not subject to root-gall. 



3. By trapping the worms and thus removing them mechanically froin 



the soil. 



I shall consider the last of these methods first. 



1. Trapping. — It consists in actually capturing the worms and then killing 

 them by hand or by machinery. How to capture a foe numbering millions 

 and doubly masked by being invisible and being hidden away underground 

 might well seem a puzzling question. How it was answered constitutes one 

 of the interesting passages in the history of applied science. The gall-worm 

 of the sugar-beet had long been known to be one of the worst pests of that 

 crop. Various investigations were made and various remedies tried by those 



