Johnson : Development of Saururus cernuus L 369 



the water, into which they often fall, and by which they must fre- 

 quently be transported (cp, Fig. 6). 



The inner integument is of three layers of which the inner and 

 outer are of transversely elongated cells, the walls of which be- 

 come thickened to the occlusion of the cell cavity. The cells of 

 the middle layer remain thin-walled and are crushed between the 

 other two (tin, Fig. 6 — the whole thickness of this integument 

 indicated in solid black). The outer integument is of two layers, 

 the outer usually of larger cells, both with thin walls {pin, Fig. 6). 

 These two layers appear as a whitish filmy coat over the dark 

 inner integument when the carpel is removed from the ripe seed. 

 At the base of the ovule a mass of chalazal cells becomes greatly 

 thickened in the ripe seed to complete the testa in this region (Fig. 6). 



The Germination of the Seed 



The exact time and rate of sprouting under natural conditions 

 has not been observed as yet, since the plants under observation 

 near Baltimore failed to develop good seeds last season. Fruits 

 obtained on the grounds of the New York Botanical Garden were 

 kept in moist Sphagnum at a low temperature, from January to 

 May, without showing any inclination to germinate. This may 

 possibly have been due to the absence of light, though other ex- 

 periments indicate that other factors were concerned. Some of 

 the fruits were placed in damp Sphagnum, others in water, and 

 still others in soil. All were given plenty of light and kept at a 

 temperature of twenty five degrees centigrade, but none of these 

 gave any external indication of sprouting, and sections showed 

 that no appreciable change in the form or relation of embryo, en- 

 dosperm and perisperm occurred during two months' time. 



About the first of April, however, all the seeds that had been 

 kept warm and given light and air, began to sprout freely. Then 

 it was found that at this time the seeds that had been cool and 

 dark also sprouted readily when given light and heat. These 



observations seem to show that changes occur here, not morpho- 

 logical, but probably of a chemical nature, such as are known to 

 occur in many other seeds, and that these changes can take place 

 under quite different conditions of light and temperature. 



A careful study of the processes of germination shows that the 



