WHITE-PIXE BLISTEII RUST. 17 



as the safest place for such work at that time. In midsummer, 1916, 

 before the disease was fairly started on the bushes on the island, it 

 was found to be pretty generall}" distributed over New England on 

 Ribes, having plainly been widely disseminated there before the 

 Block Island experiment was started. Conditions on the island are 

 not very favorable for Ribes and are decidedly unfavorable for white 

 pines. Pinus nigra var. austriaca is the only pine seen on the island, 

 and it occurs only in protected hollows. 



Table I presents the general results of tests made in the green- 

 house where inoculations were made with both a3ciospores and 

 urediniospores. A preliminary statement has been published, giv- 

 ing the earlier results of this work (147). This table is to be inter- 

 preted as follows: 



In the columns headed "Susceptibility," a single cross (X) means slight infection, 

 two crosses (XX) mean a medium degree of infection, and three crosses (XXX) mean 

 heavy infection. 



There are no means of knowing what degree of susceptibility was indicated by 

 the experiments of European and Canadian investigators, whose results are included 

 in section 1 of Table I. The foreign expeiimenters are first listed alphabetically 

 under each species of Ribee, then the work done in this country is given in a similar 

 manner. The vaiietal tests (sections 2 to 4 of Table I) are wholly the work of the 

 Office of Investigations in Forest Pathology, there being practically no data in 

 foreign literature on inoculations of horticultural varieties. 



In numerous cases but a single test has been made as yet; but the 

 general behavior of the tested plants in the spread of the fungus, 

 the type of its fruiting, etc., during the rest of the season are con- 

 sidered in the fuial estimate of susceptibility. When a single test 

 has been made under favorable conditions, it is believed that the 

 results are fairly indicative of the susceptibility of the species or 

 variety tested. Many tests were made under conditions known to 

 be adverse, and the negative results are largely due to tliis cause alone. 

 But these tests are given with the others to give some idea of what 

 has been done. Scanty numbers of tests are often due to the Ribes 

 stock dying before a second test could be made. This is true of 

 many cuttings which made a weak start and did not survive potting. 



In sections 2 to 4 of Table I, relating to the varieties of Ribes, an 

 attempt has been made to use varietal names that are intelligible to 

 horticulturists as accepted by the American Pomological Society. 

 Acknowledgment is made to the Ofiicc of Horticultural and Pomo- 

 logical Investigations of the United States Department of Agriculture 

 for help in this matter. In some cases varietal names are given 

 which are considered to be synonyms of others in the list; but in such 

 cases the stocks used under the two names were evidently different. 

 Varieties and even species of Ribes supplied by nurserymen are often 

 other than what they purport to be, and in some cases they are 

 mixtures of two or more distinct things; hence, the varietal names can 

 not be taken as being absolutely reliable. 



46103°— 21— Bull. 1)57 2 



