236 



SCIENCE. 



[N. S. Vol. XVI. No. 397. 



These experiments have for the most part been 

 conducted in the greenhouse, where there was 

 an advantage to be derived from a partial con- 

 trol of the heat, light, moisture, wind, etc., 

 especially in the control of natural infection. 

 The inoculations have been made after the 

 usual maimer by spraying the plants and plac- 

 ing the spores on the moistened stems or leaves 

 of seedlings or established plants. The first 

 inoculations on asparagus were made Decem- 

 ber 12, 1900, with uredospores obtained from 

 the then dead plants in the field. Spores, 

 obtained in the field on March 28 and April 

 24 following, gave successful inoculations also, 

 the uredospores having retained their vitality 

 during the winter when protected by the un- 

 broken epidermis of the asparagus. 



The period of incubation in the greenhouse 

 has varied from eighteen to eight days. What 

 it is in the field has not been determined, but 

 it probably varies there as it did in the green- 

 house. 



Since the rust was dependent upon its host 

 for its food, it seemed that the conditions of 

 heat, sunshine and moisture necessary for the 

 growth of the asparagus ought to have some 

 effect on the development of the rust as indi- 

 cated by its period of incubation, or the time 

 that elapsed between the time of inoculation 

 and the first appearance of the uredospores 

 through the ruptured epidermis of the aspar- 

 agus. 



In these experiments, the variation could 

 not have been due to a lack of moisture, for 

 at times some of the plants were often kept 

 too wet, as indicated by the growth of algae on 

 the surface of the soil. The plants, of course, 

 did not grow well, neither did the rust, the 

 sori being small and the spores light-colored. 

 The two factors of heat and sunshine are so 

 closely related to each other that it would be 

 almost an impossibility to separate them. 

 During the spring and summer the sun was 

 the only soiirce of heat in the greenhouse. 



When the temperature, the number of hours 

 and the intensity of the sunlight were low dur- 

 ing the winter months, from fourteen to 

 seventeen days were required for the sori to 

 appear ; during the spring months, when there 

 was a gradvial increase in the number of hours 



of sunshine and the intensity of the sunlight, 

 the number of days was reduced from twelve 

 to eight. When the mean daily temperature 

 in the greenhouse was 69° and the average 

 hours of sunshine* were five, it required four- 

 teen days for the sori to appear after an 

 inoculation was made; and when the tempera- 

 ture increased to 76° and the number of hours 

 of sunshine increased to 6.3, only eight days 

 were required; the period of incubation being 

 in each case inversely as the temperature and 

 the hours of sunshine. 



The susceptibility of the plants to inocula- 

 tion depended to a large extent upon their 

 vigor and rate of growth. Attempts were made 

 repeatedly, not only on the asparagus but on 

 several species of the Caryophyllaceag, to in- 

 oculate them when they were not growing 

 well. It was tried on repotted plants, those 

 attacked by insects, slow-growing seedlings 

 and mature plants, with little if any success, 

 while out of forty-two plants which were ma- 

 king a vigorous growth and inoculated at the 

 same time 3Y, or 90 per cent., of them pro- 

 duced sori. 



Successful inoculations with uredospores 

 were made on the principal varieties of the 

 garden asparagus (Asparagus officinalis) and 

 the following species grown for decorative pur- 

 poses: A. plumosus nanus, A. hroussonetii and 

 A. verticillatus. 



It was a difficult matter to germinate the 

 teleutospores by the methods employed. Dur- 

 ing the spring spermogonia were produced on 

 seedlings of A. officinalis in seven days, fol- 

 lowed by secidia. Infection from the secidio- 

 spores was brought about by sprinkling the 

 plants with the hose. Spermogonia were also 

 produced on Smilax (A. medeoloides) , but nc 

 secidia. 



In many instances teleutospores have fol- 

 lowed the production of uredospores, thus 

 giving all the stages of the asparagus rust 

 from inoculations. 



The most unexpected results have been 

 obtained from inoculations made on the com- 



* These results were obtained from the observer 

 for the Weather Bureau at Lincoln, Nebr., and 

 represent the time when the sun was actually 

 shining. 



