108 



GROWTH OF PLANTS 



the medium when seeds are kept in moist peat moss or soil at favorable 

 temperatures. The coats soften and readily disintegrate, thus removing 

 a mechanical barrier in seed germination. 



"The coats of seeds kept free from fungi, but under similar conditions 

 of moisture and temperature, do not undergo these changes. 



"In seed coats exposed to sulphuric acid for different periods of time, 

 the fiber tissue is reduced in amount in proportion to the length of expo- 

 sure. The longer exposures favor the development of fungi in subsequent 

 holding in peat moss at 30° C. Too long exposure is disadvantageous for 

 seed germination, probably because of excessive development of fungi, 

 possibly because of change in the inner cuticle rendering it non-resistant 

 to fungus entrance. 



"The fibers of the coat and the thin-walled tissue in the placenta region 

 are permeable to water, as indicated by entrance of salts and methylene 

 blue. The inner cuticle is apparently impermeable. Both inner and outer 

 cuticles seem to be barriers to the progress of fungi under normal condi- 

 tions. 



"The embryo is small with a short suspensor radical, short hypocotyl 

 and cotyledons and an undeveloped stem tip. There seems to be a tend- 

 ency toward increase in size and differentiation with keeping in moist peat 

 moss at 5° C, which is more marked if this is subsequent to exposure to 

 sulphuric acid and an interval at 30° C." 



OUTER FIBERS 



CRYSTAL LAYER 

 JNNER FIBERS 



ENDOSPERM 



INTEGUMENT 

 EPIDERMIS 



EMBRYO 



THIN WALLED 

 TISSUE 



Figure 40. Diagram of median longitu- 

 dinal section of Symphoricarpos racemosus 

 seed (16.5 X). 



Later, Flemion and Parker ^'^ showed that the germination behavior of 

 Symphoricarpos orhiculatus is similar to that of S. racemosus, except that 

 the former responds to a higher stratification temperature. Flemion "' 

 found that addition of nitrates or other nitrogen compounds to the peat 

 during the warm temperature period in the peat hastened the decomposi- 

 tion of the tough seed coats. It is a well-established fact that when micro- 

 organisms decompose cellulosic materials in the soil, they consume much 



