828 WEED FLORA OF IOWA 



the highest in clover, 97.25 per cent. Of the sixty samples of red 

 clover examined for dodder, twenty-eight were free. The most 

 common species was clover dodder, although others were also found. 

 One lot of alfalfa from South America contained the Chilian 

 dodder. In this investigation as in others, he emphasizes the im- 

 portance of determining the kinds of weeds found in the seed, 

 thus: In Australian orchard grass the hairy brome grass was 

 common, and in North American seed, orchard grass, timothy, blue 

 grass and tickle grass. 



The work of Settegast treats extensively the subject of agricul- 

 tural seeds and seed testing, especially with reference to vitality 

 and seed production. 



Vandevelde's work treats of the morphology and physiology of 

 germination and includes a splendid bibliography. 



Attention should be called to the excellent contributions of 

 Wollny whose reports of his splendid work on seeds and the care 

 of agricultural crops often give considerable detail on the ger- 

 mination and viability of various agricultural seeds. 



Kienitz gives a detailed account of the methods to be followed 

 in the study of germination of seeds. 



Fruwirth carried out a study on the color and specific gravity 

 of clover seeds. He found that the dark violet seeds were heavier 

 than the light colored ones of the same head, and perhaps had 

 greater germinative energy. 



Samek carried on an experiment, testing seeds for a period of 

 eleven years, showing the results of germination after the first and 

 eleventh years. 



Hiltner in a somewhat recent paper discusses the limitations of 

 seed testing and the importance of obtaining pure seed. 



H. von Guttenberg gives the description of five species of 

 Cuscata and a key for their identification. Von Degen notes the 

 germination of dodder under varying conditions. Kinzel has made 

 a study of the effect of freezing seed and its bearing upon agri- 

 cultural weeds. Pieper discusses the method of testing the ger- 

 mination of seeds and presents a new method of determining the 

 germination of grass seed. Dorph-Petersen gives a summary of 

 seed tests carried on by the Danish Seed Control Station, during 

 which 9,024 samples of clover, grass, and other seeds were analyzed. 

 The paper gives a list of weed seeds found and includes notes on 

 germination and purity. F. G. Stebler, of the Zurich Seed Control 

 Station, Switzerland, gives the results of tests made of 10,335 



