290 BOTANICAL GAZETTE [april 



and finally by a transfer to a still higher temperature in order to 

 permit vigorous growth. These conclusions are drawn from the 

 facts that (i) seeds after-ripened at 0-2° C. did not germinate until 

 transferred to a temperature of 10-12° C; (2) although germination 

 began at the higher temperature, growth soon ceased; and (3) 

 seeds which had been after-ripened and which had begun to ger- 

 minate at 4-6° C. grew well when transferred to soil in the green- 

 house. Table IV suggests that one-year old seeds are better than 

 fresh, but additional data upon this point are desirable. A nursery- 

 man with many years' experience in the growing of trees and shrubs 

 states that if Tilia seeds are allowed to become dry between the 

 time of maturing and the time of layering a low percentage of 

 germination results. On the other hand, if a high moisture content 

 is maintained during this period no difficulty in germination is 

 encountered. Up to the present time the author has been unable 

 to obtain seeds which at the time of gathering had a moisture 

 content of more than 10 per cent, and it seems probable that the 

 water content of Tilia seeds is generally low at harvest time. While 

 these seeds do not after-ripen to any considerable degree in air- 

 dry storage, those that have been in the air-dry condition for a year 

 after-ripen perfectly when put in a moist germinator at a low 

 temperature. There seems to be no injury, therefore, even from 

 protracted air-dry storage. No discussion is necessary to show that 

 field conditions are not those most favorable for the obtaining of 

 high percentages of. germination. Neither does the nurseryman, 

 when layering seeds, control the temperatures to the extent 

 necessary to secure maximum results. 



Hydrogen ion concentration. — The determinations of the 

 hydrogen ion concentrations were made with the hydrogen electrode. 

 Twenty seeds were pulverized in a mortar, and, except in instances 

 to be noted later, 25 cc. of water added. The temperature varied 

 from 27 to 33° C, but in every case the necessary correction was 

 made. The determinations were made upon the seeds in the unaf ter- 

 ripened condition, after-ripened but not germinated, with hypocotyl 

 2 mm. to 5 mm. long, and with hypocotyl 0.5 cm. to 2 cm. long. 



EcKERSGN (8) has already shown that the acidity of the hypo- 

 cotyl of Crataegus increases as after-ripening progresses. Her 



