July 15, 1921 
Effect of Crowngall Inoculations on BryopJiyllum 597 
that there are totipotent cells—in the leaf axils and in the leaf notches 
of Bryophyllum —there I have got the same results with crowngalls as on 
other plants. 
I undertook to test my conclusion as to the rarity of totipotent cells 
in the midrib of Bryophyllum calycinum in another way—that is, on 150 
well-developed leaves by means of sand-bed experiments. The margins 
were trimmed away and after some days the leaves were removed from 
the plants and bedded on damp sand, with the undersurface down and 
petiole buried. Just before this was done the midribs were cut crosswise 
in from 4 to 12 places, depending on the size of the leaf. After six weeks 
they were removed and examined. Of these leaves, 27 per cent devel¬ 
oped roots (and sometimes shoots) from the base of the petiole, showing 
that totipotent cells are of fairly frequent occurrence in that organ, and 
10 shoots appeared on the margin of leaf blades in spite of the fact that 
they had been trimmed, but, with exception of two cuts on one leaf 
where incipient roots appeared, none whatever (either roots or shoots) 
appeared on the cut midribs, although the conditions were favorable and 
there were at least 1,000 opportunities. This tends to confirm the con¬ 
clusions derived from the crowngall inoculations. I conclude, therefore, 
that shoots are rare in the midrib tumors for the sole reason that totipo¬ 
tent cells are rare in such places. Yet if organs are developed directly 
from tumor cells, as Mr. Levine maintains, then why in the presence of 
such an abundance of tumor cells in active growth are shoots and roots 
so rare in midrib tumors on Bryophyllum ? These tumors grow as vigor¬ 
ously as axillary tumors on Bryophyllum or as midrib tumors on tobacco, 
and should we not expect to find shoots as common in the former as in 
the latter, if this hypothesis is correct ? 
The exact nature of the stimulus that sets the leaf-notch buds growing 
in crowngall inoculation may be left for discussion elsewhere. It is 
sufficient here to have established that, contrary to Mr. Levine’s state¬ 
ments, a distinct crowngall stimulus exists for the dormant buds of 
Bryophyllum. 
