464 



Garden and Forest. 



[Number 352. 



The leaves of Primus demissa are affected with an Exoascus, 

 which may be the same as this species which curls the leaves 

 of P. serotina. Sterile conditions of an Exoascus have been 

 found on the leaves of P. Virginiana near fthaca, New York, 

 which may probably belong also to this species. The twigs 

 are sometimes deformed and strongly curled, but thus far no 

 mature condition of the fungus has been observed by myself. 



Exoascus communis, Sadeb., is found on several species of 

 Prunus, affecting the fruits or young ovaries in the same man- 

 ner as E. Pruni does Prunus domestica. It is found on P. 

 Americana, P. nigra, P. pumila and P. maritima. 



Exoascus mirabilis, Atkinson, originates a peculiar deformity 

 of the leaf-buds and twigs of Prunus angustifolia and P. hor- 

 tulana. The buds and twigs are transformed into a large, 

 usually clavate, mass of spongy tissue resembling in consist- 

 ency that of the plum pockets. Frequently these structures 

 are hollow. The fruit of the fungus is borne upon the surface 

 of the affected portions. Sometimes the entire leaf-bud is 

 affected so that none of the leaves are expanded, and in other 

 cases the leaves may be partly expanded when the fungus 

 makes the serious attack, and the deformed bud will present 

 leaves partly or fully expanded. A variety of this species 

 attacks the fruit, affecting usuallv only one side of the fruit, 

 and causing it to turn or twist to one side. Unless a large por- 

 tion of the surface of the fruit is affected, there is no cavity in 

 the deformity. The variety has been named E. mirabilis, var. 

 tortilis, Atkinson. 



Exoascus longipes, Atkinson, is a second species producing 

 plum pockets of the fruit of Prunus Americana in the vicinity 

 of Ithaca, New York. It differs from the above-named spe- 

 cies, affecting the fruit by the very long stalk-cells of the asci, 

 which penetrate far between the cells of the host. 



Exoascus rhizipes, Atkinson, produces deformities of the 

 fruit and leaf-buds of Prunus triHora, similar to those of P. 

 angustifolia by E. mirabilis, but is differentiated from that spe- 

 cies by the very long and much-branched stalk-cells, which 

 penetrate even farther between the cells of the host than is the 

 case with E. longipes. The specimens were collected at 

 Auburn, Alabama, on the farm of the State College. 



A third species is found upon Prunus Americana, this time 

 upon the leaves, causing a series of very fine folds, with the 

 asci developed upon the underside. Frequently the ends of 

 the twigs are somewhat deformed, and then especially are the 

 petioles and bases of the leaves brought under contribution to 

 the fungus, resulting in the blackening and ultimate death of 

 the parts affected. This species has been named Exoascus 

 decipiens, Atkinson. The half-grown fruit of Prunus Ameri- 

 cana is also affected by an Exoascus which grows only in the 

 superficial tissues, causing wart-like prominences upon the 

 surface. The asci are near the type ot those upon the leaf, 

 and not those of the other species occurring on the fruit of P. 

 Americana. The material thus far examined has not been 

 sufficient to determine whether or not it is a distinct species 

 from that growing upon the leaves, though there seem to be 

 some differences. For this reason it is at present placed as a 

 variety of E. decipiens, namely, var. superficialis. 



One of the most interesting of the species occurring on the 

 fruits is Exoascus cecidomophilus, Atkinson. This occurs 

 upon the fruits of Prunus Virginiana which have been 

 deformed by a cecidomid larva. The insect produces an 

 elongated and hollow gall, which is open at the proximal end. 

 The gall is smooth within, and the tissue is hard, in contradis- 

 tinction to the spongy tissue of the common plum-pockets. 

 The fungus grows in the superficial tissues of the gall, proba- 

 bly only over a portion of the surface. 



These fungi are communicated to other trees in two ways, 

 by infection from the spores and aiso by budding in nursery- 

 stock as well as by budding into trees in the orchard. This, of 

 course, is not done knowingly by the nurseryman, for at the 

 time that the buds are selected for budding all of the leaves 

 which are affected have probably fallen from the trees. If the 

 trees were carefully examined during the early part of June or 

 the latter part of May, and the unaffected ones selected at this 

 time for obtaining the buds, this common source of infection 

 might be prevented. 



Cornell University. George F. Atkinson. 



A Serious Blight of Cosmos. 



ONE of the best of the plants which flower out-of- 

 doors in autumn until the coming of hard frosts, the 

 hybrid Cosmos, has been attacked by a blight this year, 

 which is already serious, and threatens to become general. 

 A mildew (Erysiphe Cichoracearnm) so abundant upon 

 many other of the Composita? is frequently seen upon the 



foliage of the Cosmos, but it is to a niuch more deeply 

 seated fungus that reference is here made. The first effect 

 of this enemy is seen in the brown discoloration of the 

 stem or branches. There seems to be pt>, uniform place or 

 method of attack, but it is apt to get a foothold at the tips 

 of a stem that has been pinched off, ancl.spread from there 

 to the branches that develop below. The growth of the 

 parasite so weakens the branches at thejr point of union 

 with the main stem that they frequently break at the junc- 

 ture, and a diseased plant may have one or more of its 

 lower branches with their tips upon the ground while still 



Fig. 72. — Blighted Plant of Cosmus. 



attached to the main stem. In other instances the blight 

 begins midway upon the branch, and causes it to break at 

 that point. This is shown in the above figure, which is 

 from a photograph of a plant entirely ruined by the blight. 

 The peculiar way in which the fungus spreads in the stem 

 is shown in fig. 73, page 465. The darker portion is dis- 

 eased, and the blighted bases of the branches are well 

 shown upon the right side of the main stem. 



The fungus, which is a species of Phycteena, apparently 

 undescribed, after vegetating for a time, produces its pecu- 

 liar fish-hook-like spores in vast numbers in minute dark 

 pimples, and when water is applied to the pimply surface 



