7© BOTANICAL GAZETTE [ January 



put into the germinator, whether in light or dark. The removal of the 

 inner coat and endosperm is done after sterilization, and the whole process, 

 including germination, is conducted under aseptic conditions. One finds 

 this a very tedious task and the resulting germination is of a peculiar type. 

 In the light the cotyledons begin to expand and turn green. A small per- 

 centage of the roots begin growth within a week, but in a larger percentage 

 the roots begin growth only after several weeks and after the cotyledons have 

 expanded to several times their original size. Many of the radicles do not 

 grow even after two months in the germinator. In the dark the growth is 

 similar except that the cotyledons turn yellow and the radicles are even more 

 tardy in their development. The coats then seem to play an important 

 part in the delay, but the tardiness of the radicle in its development is of 

 especial interest and reminds one of the behavior of the fungus-free orchid 

 seeds, s or the upper seeds of the cockiebur with coats intact and in 76 cm of 

 oxygen pressure.* A full investigation of the physiology of the germina- 

 tion of these seeds is now in progress by Mr. W. E. Davis and myself. 



Ewart again says: "Crocker has, however, overlooked the fact that 

 both the early and late seeds of Xanthium echinatum will germinate at 

 20 to 2 5 C. if the temperature is maintained for fourteen to twenty-one or 

 more days instead of for eight to nine days." I assume that Ewart means 

 with coats intact, for that is the connection in which I have made my 

 statement. On November 5, 1908, burs of this species were collected from 

 the plants, the seeds removed from the burs, and the upper seeds soaked 

 18 hours, so as to show up any defective coats. Upper seeds with perfect 

 coats were placed between wet niters in baths; one maintained at 24-25°, 



and one at 2 7-2 8°. 



germinated. Of course 



with coats removed these seeds germinate within three days, even at 23°- 

 In collections of this species from the crop of 1 906 a small percentage of the 

 upper seed with coats intact germinated at 30 . In collections of the crop 

 of 1905, on which the work for my paper was done, the minimum tem- 

 perature for the germination of these upper seeds lay between 32 and 33° 

 even when they were kept in the germinator for a month. Ewart says 

 nothing about the time of gathering, precautions against defective coats, 

 or the percentage germinating at 20-2 5 . In the absence of all these related 

 data his statement can mean little. In X. canadense high temperatures are 

 far less effective in overcoming seed-coat effects, and here a temperature 

 fluctuating between 25° and 41° is most effective. A temperature of ^ 

 43 for a few hours is often more effective than a lower temperature for a 



s Bernard, N„ On the germination of orchids. Rov. Hort. Soc. Rep. 3rd Inter- 

 nal. Congress on Genetics 292-296. ! 9 o6. 



