1914] CROCKER &• DAVIS— DELAYED GERMINATION 289 



weighing. The permanent shrinkage in salt solution may be due 

 to a semipermeable membrane in the seed coat or to a change in 

 the water-imbibing power of the colloids of the coats and perhaps 

 of the embryo owing to the presence of the salt. A. Fischer 

 found that the intact fruits of Sagittaria were not at all injured by 

 five days' soaking in mol. copper sulphate solution. We find that 

 one month's soaking of intact seeds of Alisma (i mol. CuS0 4 ) does 

 not injure their germination, if they are thoroughly washed and 

 the coats opened before they are germinated. The opened seeds 

 grow better in o.oooooi mol. CuS0 4 than in distilled water, but 

 very little in o.ooi mol. CuS0 4 . Soaking of the intact seeds in 

 10 per cent AgN0 3 for 24 hours kills all of them. From these 

 facts it seems probable that in Alisma and Sagittaria the seed 

 coats bear semipermeable membranes akin to those found in 

 Xanthium (29) and various grasses (5, 28). 



1. Structure and michrochemistry of the seed coat. 



As the later experiments will 

 the microchemistry of the cc 

 camera drawing of a median 

 the main the coat consists of 



it is much to the point. Fig. 1 is a 

 longitudinal section of the coat. In 

 two layers of cells: the outer yellow, 

 red, or brown layer (b), and the inner colorless layer (c). At the 

 micropyle end there is usually only one layer of cells. In the region 



oimn 



layer are distinct. 



mass (/) , while the cells of the inner 



mi 



from 



As 



a consequence, the inner face in this region has a very undulating 

 appearance. When the seeds germinate after acid treatment or 

 when one picks off the coat at the micropyle end, a rather definite 

 cap is removed. The caD seems to result from the breaking at one 



more 



Inside the cellular portion 



lining mass of material 



mixture of hemicellulose and pectic material. This layer is rather 

 thick at the micropyle end of the embryo, and as thick or thicker 

 at the opposite adjacent end of the embryo. In this connection 

 it should be stated that it is common to find seeds with the 

 outer layer of cells largely abraded lying in water in the dormant 





