Nov. is, 1920 Vascular Discoloration of Irish Potato Tubers 279 



The two lots of seed stock were planted and grown in widely separated 

 regions and under distinctly different environmental conditions of soil 

 and climate, one lot being planted on a light, sandy soil, under rainfall, 

 at Waupaca, Wis., and the other on a heavy clay loam under irrigation 

 at Greeley, Colo. The identity of each plant was preserved, and fre- 

 quent records were made by the same observers in rotation in each and 

 in both regions to secure all the data possible regarding the influence 

 of the seed piece and environment and of the interrelations of these 

 upon individual plant performance, with special reference to the develop- 

 ment of pathological conditions. 



DESCRIPTION OF MATERIAL 



The material may be divided advantageously for consideration into 

 three groups, each containing several lots. The first group comprises 

 stock affected with tuber-borne diseases of undertermined origin; the 

 second lot is from healthy parentage; and the third is from diseased par- 

 entage where the malady is regarded as of parasitic origin. For brevity 

 in presentation many lots which were held separate during the investiga- 

 tion have been combined, so as to appear as a unit, whenever their origin 

 and performance made such treatment feasible. 



A brief description and index of the lots presented in the tables follows. 

 A. — Obscure disease group. 



1. Thirty-four seedling varieties originated by Prof. Wm. Stuart, 

 of the Department of Agriculture, and originally regarded as promising 

 but ultimately discarded because of the persistent reappearance of 

 destructive but imperfectly understood hereditary diseases. This 

 material had been grown at Jerome, Idaho, in 191 3 and 191 4, in the 

 pathological plots there. 



2. The progeny of 31 hills of Western Peach Blow, grown at Greeley, 

 Colo., which were suspected of Fusarium infection. This stock is now 

 known to be affected also with leafroll and mosaic and is therefore placed 

 in this group. 



3. A miscellaneous collection of 21 lots from the pathological collection 

 of the field station at Presque Isle, Me. Both seedling and commercial 

 varieties affected with leafroll. mosaic, and dwarfing diseases were 

 included. This lot was grown only at Greeley, Colo., and the tubers 

 were either planted whole, or, if they weighed over 3 ounces, they were 

 cut once crosswise into stem and apex halves. 



B. — Healthy group. 



4. A representative commercial lot of the variety Late Ohio, grown at 

 Greeley, Colo., in 191 4 and obtained from the grower. 



5. An exceptionally good commercial strain of the variety Pearl, 

 grown in Greeley, Colo., in 1914, obtained from the grower and col- 

 lected from the field at harvest time. 



