59 



this class seeds after-ripen, or get ready for germination, per- 

 fectly when stratified at 5° C. but do not do so at all in some 

 seeds when stratified at 0° C. or 10° C. One exception was 

 mentioned, Cornus Nuttallii^ which after-ripens better at 0° C. 

 than at 5° C. or 10° C. Amongst the seeds that after-ripen best 

 in stratification at about 5° C. are most rosaceous seeds, including 

 all the roses, most large rosaceous fruits (apple, peach, pear, plum, 

 cherry, etc.), Crataegus, Cotoneaster, and many other rosaceous 

 plants; Cornus florida, Tilia, Juniperus, fall-fruiting maples, 

 Ambrosia, and probably many other genera. There are probably 

 scores of genera of the temperate zone that demand stratifica- 

 tion for a period at a low temperature. The temperature may 

 fluctuate considerably during the stratification if it runs between 

 0° C. and 10° C. and averages about 5° C. It is probable that 

 in other forms than Cornus Nuttallii a temperature very near 

 freezing will be best, as 10° C. is nearly as good in some as 5° C. 



The speaker also emphasized the fact that in stratification 

 the medium is of considerable importance. A certain granulated 

 peat proved much better for Cotoneaster and for certain roses 

 than sand. 



In stratifying good seeds no doubt the main trouble in the 

 stratification of the seeds mentioned above and probably in many 

 others will be overcome by proper regulation of the temperature 

 and by proper choice of the stratification medium. Of these 

 the regulation of the temperature is of prime importance. 



The length ot time necessary for stratification at this low 

 temperature varies greatly with different genera and even 

 different species of the same genus. Apple seeds and Rosa 

 inultiflora seeds require 60 to 75 days; Rosa rugosa, Rosa rubigi- 

 nosa, Cornus florida, Tilia americana, Juniperus, and various 

 species of maple require 3 to 4 months. Some roses, Crataegus, 

 and others require 6 months or more. 



The speaker emphasized the fact that freezing temperatures 

 were of no value in furthering the germination of this class of 

 seeds. Freezing is either indifferent in its effect or actually 

 injures the seed, especially in the latter stages of stratification. 

 He believes that commercial cold storage can be economically 

 adopted for the stratification of many seeds of this class. 



In the class of seeds with dormant differentiated embryos Dr. 

 Crocker spoke of the failure of chemical forcing agents, because 



