SWEET-CLOVER SEED. 3 



in 1904 died, Kirchner concluded that the flowers of M. officinalis 

 were especially sensitive to inclosure in nets and that the failures to 

 obtain more than a very few seeds on protected racemes in Darwin's 

 experiment and in his first experiment were due to this cause. 



According to Kerner '(17, v. 2, p. 399) the peas and lentils (Pisum 

 and Ervum) and the different species of horned clover and stone 

 clover (Lotus and Melilotus) as well as the numerous species of the 

 genus Trifolium and also many others produce seeds when insects 

 are excluded from the plants, and only isolated species of these 

 genera gave poor yields without insect visitation. 



OUTLINE OF POLLINATING EXPERIMENTS. 



The yield of sweet-clover seed varies greatly from year to year in 

 many parts of the United States. It has been assumed that this 

 variation was due to climatic conditions, as excellent seed crops were 

 seldom harvested in seasons of excessive rainfall or of prolonged 

 drought just preceding cr during the flowering period. The lack of 

 a sufficient number of suitable pollinating insects also was thought 

 to be an important factor in reducing seed production. This was 

 especially true where the acreage of sweet clover was large and where 

 few, if any, honeybees were kept. 



In order to obtain data upon the factors influencing the yield of 

 seed, a series of experiments was outlined to determine (1) whether 

 the flowers are able to set seed without the assistance of outside agen- 

 cies, (2) whether cross-pollination is necessary, (3) the different kinds 

 of insects which are active agents in pollinating sweet clover, and (4) 

 whether a relation exists between the quantity of moisture in the soil 

 and the production of seed. 



The racemes containing the flowers which were to be pollinated by 

 hand were covered with tarlatan before any of the flowers opened and 

 were kept covered except while being pollinated until the seeds were 

 nearly mature. This cloth has about twice as many meshes to the 

 linear inch as ordinary mosquito netting and served to exclude all 

 insects that are able to pollinate the flowers. When entire plants 

 were to be protected from all outside agencies, cages covered with 

 cheesecloth, glass frames, or wire netting were used. 



A preliminary study of the pollination of Melilotus alba and M. 

 officinalis showed that both were visited by the same kinds of insects 

 and that both required the same methods of pollination in order to 

 set seed. On this account M. alba was used in most of the experi- 

 ments reported in this bulletin. Where M. officinalis was employed 

 it is so stated. 



