398 Plant Physiology 



and weight of the seed from similar individuals. Trabut 1 

 found it possible to effect a separation into heavy and 

 light sorts through the capacity of these two kinds, re- 

 spectively, to sink or float in water. It was found that the 

 heavy seed produced plants which were greener, more 

 vigorous, and of larger size. Shamel has made further 

 studies of this relation, separating, by means of a current 

 of air, the seeds into three categories - - heavy, medium, 

 and light. Samples of these seed were germinated, and 

 the accompanying illustration shows the relative vigor of 

 the plants resulting from the different grades. 



LABORATORY OR SUPPLEMENTARY WORK 



Write a report upon the vitality of seed as affected by 

 methods of harvesting and storage, consulting the literature 

 accompanying this chapter, also such of that contained in re- 

 cent volumes of the Experiment Station Record as may be 

 readily available. 



REFERENCES 



CROCKER, W. Role of Seed-coats in Delayed Germination. 



Bot. Gaz. 42:265-291, 1906. 



DE CANDOLLE, A. P. Physiologie vegetale. 2 : 618, 1832. 

 DETMER, W. Vergleichende Keimungsphysiologie. 565 pp., 



1880. 

 DUVEL, J. W. T. The Vitality and Germination of Seeds. 



Bur. Plant Ind. U. S. Dept. Agl. Bui. 58:96 pp., 1904. 

 - The Vitality of Buried Seeds. Bur. Plant Ind. U. S. Dept. 



Agl. Bui. 83 : 22 pp., 3 pis., 1905. 

 HICKMAN, J. FREMONT. Field Experiments with Wheat. Ohio 



Agl. Exp. Sta. Bui. 129 : 27 pp., 1901. 



1 Trabut, L., Bui. 17, Service Botanique de 1'Algerie. 



