Further anent “frost flowers” 
An explanation of frost crystals on dried plant stems 
H. M. JENNISON 
In Mr. Raymond H. Torrey’s article published in TORREYA, 
for Jan.-Feb., 1931, we found a very interesting and accurate 
account of a phenomenon not uncommonly observed in the 
vicinity of Knoxville, Tennessee. At least six of my colleagues 
and students have seen and speculated on the formation of 
similar ice ribbons. With us, such ice ribbons have been ob- 
served on the lower internodes of the main stem of such coarse 
herbs as Verbesina occidentalis, V. virginica, and Pluchea peti- 
olata. Mr. Torrey concludes with the intriguing question, ‘Can 
anyone offer an explanation as to the mechanics of this phen- 
omenon?” 
The following explanation of the phenomenon in question 
has developed as a result of the observations made at times dur- 
ing the past three years. No opportunity has been available for 
experiments, and I do not suppose that this offering can with- 
stand the critical gaze of a physico-mechanical engineer. Per- 
haps, however, it may be sufficiently reasonable to satisfy the 
average naturalist-observer. 
In the first place, it is important to note that phenomena 
similar to the one described by Mr. Torrey, as seen by us, occur 
during the late fall and mid-winter months. By that time suc- 
cessive frosts have defoliated the vegetation and cut down the 
tender twigs. When and wherever we have found these fantastic 
ice-crystal ribbons they were of considerable size and occurred 
near the base of the stem. We have observed them in actual 
Process of development. With few exceptions the phenomena 
have been noted early in the day, or if later, only on north slopes 
where the plants were shaded until late in the afternoon. Up to 
the dates of observation, the temperature had not been low 
“nough to cut down the stout stems of such coarse herbs as those 
-amed above, much less kill the roots. Nor was the ground 
frozen, In fact, except in the surface layers the soil was moist 
sal warm enough for biological activity. Under the cise 
nvironmental conditions, the root systems of these pianis w 
still functioning quite vigorously and a considerable root- 
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