378 BOTANICAL GAZETTR [November 



day germination was well started, as shown by the length of the 

 cotyledons and their response to gravity. In two days the growth 



+ 



was very marked. 



It might be urged that breaking the coats leads to increased oxygen 



w 



supply and for that reason brings about germination. This is not at 

 all probable for two reasons: hrst, increased oxygen pressures never 

 bring about germination when the coats are intact; and second, 



these seeds require very little oxygen for germination. If the coats 

 are ruptured, they will germinate if placed in water that has been 

 previously boiled and covered with liquid paraffin. That the coats 

 hinder germination by limiting the water supply is made evident 

 by the fact that the cotyledon begins to project beyond the coat very 

 soon after the latter is ruptured. In this experiment it seems impos- 

 sible to justify the assumption that the protoplasm is in a dormant 

 state or that the appH cation of any external ions are necessary to 

 start germination. 



It is of interest to determine what structures surrounding the 

 embr}^os limit the water absorption. In Sagittaria and Alisma there 



is an outer husklike exocarp and an inner hard endocarp. The 

 removal of the exocarp did not increase the per cent, of germination, 

 provided the endocarp was not injured in its removal. In Eich- 

 hornia the embryo is surrounded by a rather thick endosperm which 

 is covered by a hard, fluted, brown seed coat. If the coat is broken 

 at the side, it leads to a rather slow germination of over 50 per cent, 

 of the seeds. If the coats are ruptured where the cotyledons naturally 



00 



germinate with remarkable promptness. This leads one to conclude 

 that the hard coat chiefly Umits water absorption, but that the endo- 

 sperm too retards it. In the Potamogetons it is the hard stony coat 

 that limits water absorption. 



Alisma are nm 



set rather close, and are then placed in water, a large per cent, wnll 



grow 



marked 



the embryos. These seeds will also germinate after considerable 

 time if planted in rich humus that is decaying by reason of abundant 

 moisture and high temperature. 



In the light of the work of Muller and Fischer two questions 



(? 



