284 



This rust was collected on an isolatotl clump of Panicum virgatum, in 

 the same region as that in which P. vexans was found. The date of the 

 formation of teleutospores was not obtained owing to the destruction of 

 the grass by fire. 



8. Aecidium Pammelii Trelease. On Euphorbia corollata L. Tippecanoe 



County. 

 This aecidium was collected June 9, 1901, on plants of E. corollata, which 

 were growing in close proximity to the clump of P. virgatum that was 

 affected with the rust P. panici. The absence of any other aecidium sug- 

 gested to the writer that possibly this was the aecidial stage of P. panici. 

 'Accordingly some of the affected Euphorbia leaves were collected and in- 

 oculations made upon potted plants of P. virgatum in the station green- 

 house. Leaves of these plants were inoculated June 11 and 14, the latter 

 being made with freshly collected material. In each instance well-devel- 

 oped uredosori were obtained in eight days from the time of infection. 

 As both inoculations were entirely successful, it would appear reasonably 

 certain that A. Pammelii on E. corollata is the aecidial stage of P. panici 

 on P. virgatum. 



9. Aecidium physalides Pk. On Physalis heterophylla Nees. Tippecanoe 



County. Collected May 22, 1901. 

 The writer wishes to acknowledge his indebtedness to Dr. Arthur for 

 the determination of the rusts. 



Effect of the Composition of the Soil "Upon the Minute 

 Structure of Plants."^' 



Herman B. Dorner. 



The growth and distribution of plants are dependent upon four fao 

 tors, namely, light, temperature, moisture and soil. Under moisture are 

 included both that of the soil and that of the atmosphere. Soil and mois- 

 ture may well be treated together, since the one is greatly dependent upon 

 the other. In the Avork carried out. the only factor which was varied was 

 that of the soil. 



The changes occurring in plant structures, due to the variation of any 

 of the.se factors, may be divided into two groups. These may be con- 



••'An abstract from a thesis presented to the Faculty of Purdue University for the degree 

 of Master of Science. 



