IvEAF Curl and Plum Pockets. 321 



ber of the cells of the diseased portion causes that part of the leaf 

 to arch upward or downward in a series of irregular folds, or a 

 somewhat circular spot becomes strongly arched in one direction 

 forming a deep, wide mouthed pocket. The twigs become en- 

 larged in diameter and variously contorted, or an early develop- 

 ment of the buds is stimulated producing what are commonly 

 called "witches brooms." The fruit becomes transformed into 

 a large spongy mass of tissue, which is hollow and devoid of the 

 " stone " or " pit ; " or only one side of the fruit is affected when 

 irregular one sided swellings of similar tissue are developed. The 

 floral envelopes in some species partake also of the hypertrophy, 

 and in other cases only the superficial portion of the fruit is aflfected 

 when the ' ' stone ' ' is normally developed. In the latter case 

 sometimes a warted condition of the fruit appears- The young 

 leaf buds of some species are transformed into a large spongy 

 hollow mass, much resembling in texture the tissue of the " plum 

 pockets." A number of these characteristic hypertrophied parts 

 of various plant organs are illustrated in photographic reproduc- 

 tions in Plates I-X. 



Mycelium. In all of the species at present known on the genus 

 Primus, with one exception,* the mycelium penetrates to some 

 depth in the tissues, but it is always intercellular. It is quite 

 characteristic and can usually be readily differentiated from the 

 mycelium of other fungi when examined in situ. It is very irre- 

 gular in its course and the size of its cells. These are cylindrical, 

 oblong, clavate, or oval, and are joined in an irregular chain 

 without order between the cells of the host. The mycelium may 

 be quite abundant in some species so that when the other intercel- 

 lular substances and portions of the cell walls of the host are dis- 

 solved out by the use of chloral hydrate, and difierentiated by the 

 use of some of the stains like eosin,"it presents a very intricate 

 network of threads. In other species or in parts of the plant 

 not so seriously affected, or in parts where the mycelium is pass- 

 ing the winter, it is more scanty, frequently consisting of isolated, 

 oval or irregularly oblong cells. 



*Exoascus minor Sadebeck, Kritische Untersuch. ii. d. durch Taphrina- 

 Arten hervorgebr. Baumkrankheiten. Abgedruck. a. d. Jahrb. d. Hamb. 

 Wiss. Anst. VIII, 1891, p. 24. 



