638 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



the disease becomes very conspicuous because of the shot-hole" 

 effect on the leaves, produced by the dropping out of roundish areas 

 of diseased tissue ; from the leaves of other species the spots do not 

 drop out, and in such cases, as a rule, the leaf tissue is not killed to any 

 appreciable extent, but in cases of severe attack the leaves turn yellow 

 and drop prematurely, thus interfering with food production and the 

 future welfare of the tree. Although " shot-holes " are produced in the 

 leaves of stone fruits by various organisms, or even by mechani- 

 cal injury or by spraying with poisonous solutions, Cylindrosporium 

 is probably the most prolific cause of this phenomenon, at least in 

 cherries, and many have attributed all " shot-hole " effects on species 

 of Prunus to Cylindrosporium Padi Karst., which, though in Europe 

 almost entirely confined to Prunus Padus, has been found in America 

 on nearly aU species of Prunus, wild and cultivated. The author finds 

 that there are at least three species of Cylindrosporium parasitic on 

 Prunus, which in their conidial stage resemble each other very closely. 

 The mycelium is intercellular, and obtains its food, in part at least, by 

 means of haustoria which penetrate the host cells, a cellulose sheath 

 being often then deposited around the haustorium by the host proto- 

 plasm. Apparently no toxin or substance injurious to the host proto- 

 plasm is secreted by the fungus, but a few of the host ceUs are kiUed 

 probably by drying. Shot-hole " formation in the leaves is appa- 

 rently correlated with the presence of the glucoside amygdalin, which 

 breaks down into simpler substances, thereby increasing the osmotic 

 pressure which causes the cells around the spot to enlarge, forming the 

 separation layer. Besides the Cylindrosporium conidia, three other 

 spore forms are found in the life-cycle of the species studied — micro- 

 conidia (spermatium-like bodies), ascospores, and apothecial conidia ; 

 all of these, except the microconidia, are known to propagate the fungus 

 on hving leaves. While the microconidia (sperm atia ?) are being 

 formed on the surface of the stroma, ascogonium-iike structures are 

 formed with their free end (trichogyne ?) projecting above the surface ; 

 but it was not ascertained whether these structures function as sexual 

 organs. The fungus passes the winter as a stroma-hke body in the 

 fallen leaves, which in the early spring develops into an apothecium of 

 the Phacidiaceous type. That the ascocarps are genetically connected 

 with Cylindrosporium is shown by their continuous development from 

 the stromata, and by producing infection and Cylindrosporium stromata 

 in living leaves when inoculated with ascospores from leaves or with 

 conidia from pure cultures from these ascospores. As to control 

 measures, the author points out that now the complete hfe-history of 

 the fungus is known it should be easier to devise control methods. 

 Since it lives over winter in the dead leaves, it is important that leaves 

 from infected trees be raked together and burnt or buried ; if ail 

 such diseased leaves are destroyed there is little danger of the disease 

 appearing the next season in such abundance as to be serious. If 

 such destruction is not feasible, spraying should begin early, at latest 

 by the middle of May. — F. C. 



