— 47 — 



The chief characteristic however was the development of a "mosaic-disease"" 

 appearance in the leaves. Certain areas in the leaves developed more rapidly than 

 the remaining parts, resulting in blister-like distortions. These areas, plainlv 

 seen in Plate VII were of a much darker green color than the surrounding areas. 

 They did not appear in any definite locations in the lamina, being sometimes more 

 numerous nearer the petiole, sometimes nearer the leaf margin and at others 

 scattered irregularly. In all cases, however, they were limited fairly clearlv b\- 

 the veins. 



As the plants neared flowering time all the younger leaves showed thesc' 

 strikingly darker areas. No insect pests were present in the greenhouse and no 

 punctures could be observed which might account for the appearance of such dis- 

 tortions. Preliminary tests showed that there was a tendency for the darker por- 

 tions to retain starch. 



Enzyme tests are in progress as also are infection trials. So far none of the- 

 latter give satisfactory results since in the, apparently successful cases there is 

 still the possibility that he pants were already affected. An interesting fact was 

 noticed with regard to the trichomes. In several cases the trichomes in the lower 

 surface of darker areas had a considerably higher anthocyanin content than nor- 

 mal. No cases of leaves showing these areas occurred in the other two varieties of 

 plants. 



All received the same treatment in every res[)ect. It may be that the '"cactus"' 

 variety is really a diseased variety. 



Snapdragon {Antirrhinum ma jus L.) 



Snapdragon rust caused by Puccinia antirrhini (D. and //.) was very abun- 

 dant, hardly a plant escaping infection. Seedling, cuttings and mature plants were 

 attacked in all stages of growth. The disease was propagated by urediniospores 

 and but few teliospores were found. The uredinia occurred on the lower surface 

 of the leaves as a rule but there were several cases of such severe infection that 

 pustules appeared on the upper surface also. 



The mycelium is localized giving rise to more or less circular diseased areas 

 on the leaves (see Plate VI) and to longer elliptical areas on the stems. The uredi- 

 niospores are from 22 to 30 by 21 to 25 microns, yellow to brown in color, echinu- 

 late to warty and possessing usually two germ spores. They germinate readily in 

 water in a few hours. Frequently they have been germinated in an hour. The 

 plants are rendered unsightly for market purposes by the presence of the uredinia 

 and when infection is severe the leaves are rapidly killed (Plate VI, Fig. 2), re- 

 sulting eventually in the death of the plant. 



It is recommended that clean seed be used as no fungicidal control is yet 

 known, so that it is difficult to obtain clean plants by propagating from cutting?.. 



Sweet Pea (Lathyrus odoratus L.) 



The greenhouse grown sweet peas suffered severely this season from 

 powdery mildew of which the causal organism is Microsphaera aln'i (IVal.) Sa!ni.. 



