19 1 2] DAVIS 6* ROSE— AFTER-RIPENING 51 



the weather is in many cases considerably higher than of those 

 kept dry. In wild rye, for instance, the dormant period was 

 reduced from 9 to 5 days, and the percentage of germination was 

 raised from 2 to 48. But the limiting factors to growth have not 

 been located in any of these cases. 



Investigation 



This work on the germination of the seeds of the hawthorn 

 (Crataegus mollis) was undertaken in order to determine so far as 

 possible the influence of the various external conditions affecting 

 their after-ripening. Hawthorn seeds usually do not germinate 

 until the second or even third year after the fruit has ripened. 

 Kuntze (14) wrote in 1881: "Hawthorn berries (Crataegus) 

 which do not germinate until the second year are peculiarly treated. 

 They are mixed with sand, thrown into a heap, and watered a few 

 times in a cold house during the winter, and sown the following 

 spring. They are turned over several times so that the pulp may 

 decompose." The Cyclopedia of American horticulture (3) also 

 refers to this delay in the germination of the seeds of the hawthorn 

 and gives the method employed in their germination essentially 

 as that given by Kuntze. 



In considering the after-ripening and germination of the haw- 

 thorn, the various structures about the seed, as the pericarp and 

 carpels, as well as the testa and embryo itself, must not be over- 

 looked. The pericarp is separated from the carpels by decay or 

 by being eaten off by some animal. It often shrivels and remains 

 intact for a considerable length of time. The carpels are bony and 

 the seed is freed only after much weathering, when the carpels 

 become more or less porous to water and are split by the swelling 

 of the seeds. Both of these structures in nature, by the prevention 

 °f a sufficient supply of water and oxygen, may tend to prolong 

 after-ripening as well as delay germination. 



Our first work was to determine the behavior of the seeds under 

 ordinary germinating conditions. To do this we removed the pulp 



and the bony 



rpel. The seeds were than placed upon wet cotton 

 both in the laboratory and the greenhouse. They 



this condition for months without 



