83 
Botanical Notes. 
Fertilization of the Borraginacece. — The change of color in various 
borraginaceous flowers would seem to bear relation to their fertiliza- 
tion. Hermann Muller remarks in Nature (May 24, p. 81), that he 
has observed that insects visit exclusively those which are red or just 
beginning to change to blue. All the blue flowers which he exam- 
ined in a locality about 2 yards broad and 20 long, where many 
hundred flowers of Pulmonai:ia were in all stages of development, 
proved to be empty of honey, and all which he observed with the 
aid of a lens, had the stigma already supplied with pollen ; so that it 
would appear that, as in Lantana and Ribes aureitm, the change of 
tint serves as a guide to insects visiting the flower. 
Contraction of Vegetable Tissues tinder Frost. — At a recent meet- 
mg of the Botanical Section of the Philada. Acad. Nat. Sciences, 
Mr. Meehan referred to a prevalent opinion that the liquid in vege- 
table tissues congealed as ordinary liquid does, and expanding, often 
caused trees to burst with an explosive sound. Mr. Meehan made 
experiments with young and vigorous trees, varying from one foot to 
three feet in circumference. They were carefully measured in early 
winter when the thermometer was at about 40°, and again after they 
had been exposed for many days to a temperature below freezing 
point, and, at the time of measurement, to 10" above zero. _ 
In no case was there the slightest evidence of expansion, while 
in the case of a large maple {Acer dasycarpum), 3 feet ii^ inches 
around, there appeared to be a contraction of \ inch. This was the 
largest tree experimented with. In dead wood soaked with water, 
there was an evident expansion ; and the cleavage with explosion 
noted in the case of forest trees in high northern regions may result 
from the freezing of liquid in the central or less vital parts of the 
trunks of trees. 
In some hardy succulents, however, instead of expansion under 
frost, there was a marked contraction. The joints or sections of 
stem in Opuntia Rafinesquii and 0. Missourtensis, shrink remarkably 
with the lowering of the temperature. As soon as the thermometer 
passes the freezing point, the shrinkage is so great that the whole 
surface has the wrinkled appearance presented by the face of some 
very aged person. A piece of Opuntia Rafinesquii, which,- in Novem- 
ber measured 4 inches in length, is but 3^ now, and is not half the 
thickness it was in the autumn. In the winter when the thermom- 
eter was down to 10° above zero, the penknife penetrated the tissue 
just as easily as in summer, and no trace could be discovered of 
congelation in the juices of the plant. Other succulents exhibited 
more or less signs of shrinkage under extreme cold. Mamillana 
Nuttallii and M. vivipara, with Echinocactus Simpsoni, a mamillose 
form, drew the mammae upwards, and had them appressed as closely 
as the spines would allow; and some species of Scmpervtvum did 
the same. This could only be accomplished by the contraction of 
the main axis from the apex downwards. Sedum Hispamcum, which 
has not a succulent axis, contracts its leaves into longitudinal 
wrinkles, presenting the appearance of being withered or dead. 
They expand again in a few days of temperature above the freezing 
