640 EXPERIMENT STATION RECORD. [Vol.43 



Sweet clover seed, H. S. Coe and J. N. Martin (U. S. Dept. Agr. Bui. S//// 

 {1920), pp. o9, pl>i. 5, figs. 6). — This bulletin comprises two parts, as follows: 



Part 1. Pollination studies of seed produetion (pp. 1-25). — This section is 

 concerned primarily with the factors underlying failure of sweet clover to 

 produce a normal seed yield through shedding of immature pods and laclv of 

 pollination. Tlie author reviews previous worlc on the same problem and 

 describes the structure and development of the flower and floral organs of 

 sweet clover. The results of studies of "^he insects most active in pollination, 

 sources of pollen necessary for fertilization, conditions of pollination required 

 for fertilization, and the relation of environmental conditions to shedding of 

 immature pods may be summarized as follows : 



Very little tendency toward sterility of ovules was observed in Melilottis alba 

 and M. officinalis. Self-pollination appeared to be as effective as cross-pollina- 

 tion in M. alba so far as the vigor of the pollen tubes and the rate of embryonic 

 development were concerned. The average dimensions of the pollen of M. alba 

 and M. offlclnaUs were found to be 26 by 32;u. and 24 by SO/i, respectively. A 

 high atmospheric humidity did not seem to check the germination of pollen. 

 This also held true with an excess of water in the stigmas resulting from an 

 abundance of soil moisture. 



Flowers fertilized with pollen transferred fronT another plant produced a 

 higher percentage of pods than when selfed or pollinated with pollen from 

 other flowers on the same raceme. Pollen transferred from one flower to 

 another on the same raceme proved more effective than when the pollen produced 

 was used to fertilize its own stigma. Self-pollination was effective, but occurred 

 spontaneously to a very small extent. 



Night-flying insects were not found to be an important factor in production 

 of sweet clover seed. Although results showed small insects to pollinate sweet 

 clover flowers freely, it was doubted whether these insects would be numerous 

 enough to pollinate sufficient flowers in a large field for profitable seed pro- 

 duction. The honeybee was the most eflicient insect pollinator of this plant, 

 and in many sections is believed responsible for the pollination of more than 

 half of the flowers. Insects more frequently visited flowers that were directly 

 exposed and readily accessible. Clear weather with vigorous insect activity 

 was accompanied by a greater effective pollination than cloudy or rainy 

 weather, when but few insects visited the flowers. 



Deficiency in soil moisture was an important factor in reducing seed pro- 

 duction. However, an appreciable increase in the water supply by rains or 

 other sources decidedly checked the fall of flowers and immature pods from 

 this cause. 



Part 2. Structure and chemical nature of the seed coat and its relation to 

 impenneable seeds of stveet clover (pp. 26-8.^). — A historical summary of the 

 contributions of earlier investigators to the knowledge of the structure of 

 legume seed coats and the cause of impermeability in seeds is presented. The 

 authors outline the methods of pi'ocedure followed and material used in a 

 series of microscopic and microchemical studies of the seed coat of M. alba 

 and M. officinalis, and describe in detail their observations on the structure 

 and chemical composition of the seed coat, the seed coat in relation to absorp- 

 tion of water, a comparison of permeable and impermeable seeds, and the 

 action of sulphuric acid on the coats of impermeable seed. 



A list of 44 titles, comprising the literature cited, is appended. 



Essays on wheat, A. H. R. Buller (Neiv York: The Macmillan Co., 1919, pp. 

 XY+S39, 1)1 s. Jf5, figs. 6). — This book comprises a short history of wheat culture 

 in Manitoba and a discussion ol the indufitry in western Canada, including 

 culture, marketing, j^nd transportation. The origin and development of Marquis 



