— 35 — 



shows a tree in lot 2, three weeks after treatment. All the leaves 

 which were mature at the time of application had fallen, yet the 

 tree appears to be in a perfectly normal condition. Fig. 2 shows 

 a tree in lot 5, three weeks after treatment. At this date the 

 growth had nearly ceased and the injury is glaring. 



Injury upon the leaf is first apparent in small and definite 

 "reddish -brown spots, which are visible upon both surfaces. The 

 centre of the spot soon assumes a lighter color, and the tissue be- 

 comes dead and translucent. The edges of the leaf become dis- 

 colored in like manner and show a tendency to curl. A close 

 observation discloses the fact that the discolorations take just the 

 shape of the drops or streaks of liquid wliich lay upon the leaf. 

 Fig. 3 shows a scorched leaf. These leaves are at once distin- 

 guished from any which may suffer from fungous troubles by the 

 absence of raised, puffed, or ragged borders about the spots, and 

 by the presence of the scorched margins. Shoots are injured in 

 the same manner as the leaves. Small bright red spots appear, 

 and blotches mark the course of the liquid as it collected and ran 

 down the stems. The whole shoot soon becomes abnormally red, 

 as if its growth were arrested. Sometimes these shoots die out- 

 right, but they oftener survive. When the spraying is very- 

 copious, so that the liquid washes the foliage, half or more of the 

 leaf may die outright without becoming much spotted. In such 

 cases the injury is quickly apparent. The liquid runs down the 

 stems freely, and they may suffer sooner than the leaves. In 

 some of our trials, the death of the shoots caused the wilting of 

 the foliage, and the leaves hung loosely for some days. Fig. 4 

 shows this sort of injury. Here it is worth noting that the upper- 

 most inch or two of the twig was not injured, owing to the wax)- 

 covering. The tips bend over, at the highest point of injury, 

 giving the tree a wretched appearance. 



Microscopic examination shows that the cell walls in the dead 

 spots retain their shape, but the protoplasm is dry and shrivelled. 

 The peach leaf has a very delicate structure, the epidermis being 

 remarkably narrow, with thin-walled cells. This delicacy of 

 structure appears to account for the peculiar susceptibility of the 

 peach leaf to injur}- : the poison quickly permeates the tissue. 



An appeal was now made to the chemist. Leaves injured by 

 London purple in lot 5 were found, after thorough washing, to 

 contain arsenic in the texture of the leaf (.0023 grams of arsenic 



