MISSOURI BOTANICAL GARDEN BULLETIN 105 
When water is forced out of the plant into a temperature 
below freezing it forms lines of ice which may soon become 
flat plates as the already-formed ice is pushed out ahead of 
the water. But it is only a peculiar combination of cireum- 
stances which makes the formation of these erystals possible. 
The soil must contain a sufficient amount of water and the 
temperature in the soil as well as in the conducting tissues of 
the plant must be above the freezing point, while the tem- 
perature of the air must be below the freezing point. With all 
these conditions favorable, frost flowers are not infrequently 
produced on the ends of cut stems of the crown beard 
(Verbesina virginica) along the path near the south end of 
the main conservatory at the Garden. Plates 31 and 32 show 
well the striking appearance of these ice flowers. Perhaps 
the best-known plant producing these structures is Heltan- 
themum canadense, commonly called ‘‘frost weed,’’ which is 
referred to in Gray’s ‘‘Manual’’ as follows: ‘‘Late in autumn 
crystals of ice shoot from the cracked bark at the root, whence 
the popular name.”’ 
NOTES 
Mr. George H. Pring, Horticulturist to the Garden, lec- 
tured on ‘‘Fall Planting’’ before the Edwardsville Wednes- 
day Club, at the High School, Edwardsville, Illinois, Octo- 
ber 3. 
Dr. George T. Moore, Director of the Garden, represented 
the Missouri Botanical Garden and Washington University 
at the dedication of the Boyce Thompson Institute for Plant 
Research, at Yonkers, New York, September 24. 
Dr. Vernon H. Blackman, professor of botany, Imperial 
College of Science and Technology, University of London, 
England, visited the Garden, October 23, and in the after- 
noon addressed the graduate seminar on ‘‘Physiology of 
Parasitism.’’ In the evening he delivered a lecture before 
the Academy of Science on ‘‘The Effect of Electricity on 
the Growth of Plants.’’ 
Recent visitors to the Garden include Prof. Delzie Demarer, 
of Hendrix College, Conway, Arkansas; Dr. William S. 
