338 



THE GARDENER'S MONTHLY 



[November^ 



is true a well-known plant-louse (Aphis Persicse) 

 does cause the leaves of peaches and those of 

 other stone-fruits to twist and curl by its punc- 

 tures ; but the appearance is distinct enough 

 from that under discussion. The leaves infested 

 b}^ insects keep their green color, are shorter 

 rolled and have not the swollen, shining appear- 

 ance as in the disease of which we speak. The 

 true cause of the latter has been known for some 

 years to be a parasitic fungus, whose mycelium 

 or vegetating threads penetrate and ramify 

 through and through the affected leaves and pro- 

 duce its fruit (spores) in a thin, whitish, powdery 

 stratum over the folia? surfaces. If a little of the 

 white coating of a diseased leaf is removed 

 upon the point of a knife-blade and placed in a 

 drop of water under a compound microscope, 

 numerous thin-walled cells of divers forms may 

 be seen. Among them some, often very many, 

 larger than the others may be observed having 

 just about the outline of a track made in the 

 mud by a flat-footed boy, the toes not appearing. 

 Through the transparent walls are to be seen 

 several small oval bodies, which he who is ac- 

 quainted with such things quickly pronounces 

 spores. Our foot-shaped cells are spore-sacks 

 or sporangia. There are plenty of them, and if 

 the disease does not spread rapidl}^ it is not from 

 the want of fertility and productiveness of the 

 parasite. 



The name very appropriately given the fungus 

 is Ascomyces deformans. 



So far nothing new has been said, though bot- 

 anists have not usually made out the penetrat- 

 ing mycelium in the leaf-tissues and have de- 

 scribed the fruit production on the surface as an 

 anomaly. Some investigations by the writer 

 have now to be added and a remedy proposed. 

 When the leaves are making their appearance 

 in Spring-time close ins.pection shovA^s that they 

 are diseased when they issue from the buds, and 

 careful examinations of their sections under the 

 microscope reveal the presence of the parasitic 

 filaments growing among and through the young 

 leaf-cells as roots grow in soil. The young leaf 

 is affected throughout or only in a given portion 

 of its area. As it expands by growth the para- 

 site is carried along and finally produces the 

 observed deformities correspondingly over the 

 whole or only apart of its surface. The disease 

 then is in the buds, and as the stem or axis on 

 which the leaves are borne constitutes a part of 

 the bud it might be inferred that this, too, is sub- 

 ject to the invasion of the enemy. This is the 



case. The young bark of a diseased iw'vj. is as 

 completely filled with the threads of the fungus 

 as the leaves themselves. It, too, is distorted 

 in its growth, thrown into ridges and swellings 

 and blister-like excresences, and when not pre- 

 vented by the firmness of the wood curls like the 

 leaves. Diseased leaves finally die, wither, and 

 drop ofT; diseased twigs when very badly atTected 

 die also, otherwise they retain the marks of the 

 destroyer throughout the season. After the time 

 of the production of spores is passed, the fungus, 

 though preserving its vitality, appears to become 

 dormant, and the injured but surviving twig may 

 now send out healthy leaves from newly-formed 

 buds. Hence it is that at one tune the leaves 

 of a tree may be blistered and distorted, at a 

 later period fresh and sound. The old leaves do 

 not recover, new ones take their places. 



If, hovvever, during the latter part of the sum- 

 mer, or at any time through the Winter, the dis- 

 eased bark of young limbs be properly examined 

 the fungus threads in a living state may be found. 

 This is a most important contribution to our 

 knowledge of the natural history of the parasite, 

 and at once suggests a feasible plan of warfare. 

 You have no doubt already anticipated this plan 

 and are wondering if it will succeed. Select by 

 close examination in Winter the portions bear- 

 ing the cause of the disease and prune them awa}'. 

 This can be done with much certainty as to the 

 results. There is no necessity of the gift of 

 prophecy to predict what trees and what par- 

 ticular branches will show the disease in the 

 leaves to be put forth the next Spring. An ex- 

 amination now of the one-year-old limbs tells 

 the story. 



It is still possible that infection may come 

 from a foreign source, as the germination and 

 development of the spore has not been traced, 

 but the slow spreading of the disease leads us to 

 hope that danger from this source is not very 

 great. If the perennial mycelium is destroyed 

 there is much to indicate a sure victory over the 

 disease. Sometimes the amount of necessary 

 pruning would be very severe, but only in trees 

 so badly infested with the preying fungus that 

 one can cut without much compunction of con- 

 science. More often very litle use of the knife 

 will suffice, and this all upon limbs of the last 

 season's growth. It would assuredly be well to 

 burn the severed branches, but their simple re- 

 moval, even though thrown upon the ground 

 beneath the tree, may and most probably would 

 be sufficient. 



