DlE-I!ArK OF APPLE TKEES. 555 



it ensued in tubes in an ice-incnl)ator, which, unfortunately, how- 

 ever, was not constant at o^ C. 



Summary. 



1. The paper describes under the term " Die-back," a disease 



in ap}>le trees caused by the fungus Cytospora leucostoina 

 (Pers.)- Sacc. 



2. The same fungus has also been reported on peach, plum, 

 and apricot trees, and investigations with the object of learning 

 in how far the fungus isolated from one host is capable of 

 infecting any of the other hosts, and in how far the fungus from 

 different hosts differ in cultural characters, are now in progress. 



3. In apple the disease usually shows as a cofifee-black 

 colouration near the soil, and from here spreads upwards, but 

 it has also iteen observed on twig'- and branches. Diseased trees 

 usuall}' die the second summer after being attacked, and on the 

 trunks canker wounds frequently result. The skin of diseased 

 branches is decidedly leathery, and later becomes loose and 

 W'rinkled. Peach trees which previously looked healthy, have 

 been observed to die suddenly fmm this disease, and on apricot 

 and plum the malady showed as a dying back of the branches, 

 accompanied by a yellowing of the leaves. The entire dead 

 portion of alTected trees later becomes dotted over w'ith the blac k, 

 silvery-capped pustules of the causal fungus, which then is 

 readily recognisable. 



4. Wherever this malady has occurred, it is recognised as 

 a most serious disease, against the spread of which all precau- 

 tions should be taken. 



5. Methods of control should be directed towards the de- 

 struction of all diseased ]:)arts of infected trees, and further 

 spread of the fungus guarded against by cleansing sprays in the 

 winter. 



6. In apple trees the fungus lives in the cells of infected 

 branches, and is also capable of invading the middle lamellae of 

 the cells. It reproduces itself by minute, hyaline, boat-shaped 

 to allantoid spores, which are borne in p\cnidia situated in lens- 

 shaped stromata, which at first are subcutaneous, and later break 

 through with a wdiitish disc. The sjwres measure 4.62 — 6.16/* 

 X T.I 55/,',. and the basidia bearing them taper towards the end, 

 and are most frequently 8.24 — 12.32^^ X i-Si^. 



The mycelium in the host is septate, branched, and the 

 indi\idual cells frequentlv swollen at the ends. 



7. The fungus has been grown in the laboratory on a num- 

 ber of media, and did well. Pvcnidia were readil}' obtained, 

 but the ascus stage has thus far failed to develope. 



8. Though the exact relation of the fungus to various tem- 

 perature-- was not determined, it ap])ears to have a wide range. 

 Growth was equally vigorotis ;it 25° C. — 30° C, and from a few 

 cultures tried also at 20° C. At 40° C. there was no growth, 



