TRANSPIRATION OF SILPHIUM LACINIATUM L. 



L. A. GIDDINGS 



State University oj Iowa, Iowa City, Iowa 



The observations here recorded were performed in an effort 

 to determine the relation of transpiration to evaporation and to 

 other factors affecting it in one of our common prairie plants, 

 Silphium lapiniatum L. Evaporation and transpiration experi- 

 ments were carried on simultaneously under various conditions 

 for the purpose of making a direct comparison of the amount 

 of loss due to each of the two processes. One set of experiments 

 was carried on in the plant physiology laboratory of the State 

 University of Iowa, and another series was carried on '}Xi the 

 field at the Macbride Lakeside Laboratory on West Lake Okoboji 

 during the summer of 1912. The detached leaves of the plant 

 were used in the transpiration experiments. 



Thanks are due Professor Shimek at whose suggestion the work 

 was undertaken and under whose directions it was carried on. 



HABIT AND STRUCTURE OF SILPHIUM LACINIATUM L. 



The reason for selecting Silphium for the transpiration experi- 

 ments was because of its xerophytic nature. It grows in places 

 where the exposure to the agents of evaporation is extreme. In 

 spite of the fact that it inhabits such unfavorable regions, it 

 grows to a height far exceeding most of the native plants of the 

 prairie regions, some specimens being found that were a little 

 over nine feet high. The leaves, especially the lower ones, are 

 very deeply incised, thus reducing the actual leaf area very 

 greatly. With the exception of the very lowest leaves, those 

 borne below the general level of surrounding vegetation, the 

 leaves decrease in size upward until the upper ones are but little 

 more than bracts. The lower leaves are long-petioled, but the 



309 



THE PLANT WORLD, VOL. 17, NO. 11, 1914 



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