74 PROCEEDINGS OF THE ACADEMY OF [1883. 



feldspathic rocks, there might result such a change as is here shown 

 to have occurred. Certain facts which the speaker had observed in 

 the serpentine deposits of Chester County, Penna., notably in 

 Brinton's quarry, indicate that^a change from a granitic dyke into 

 serpentine Is not an uncommon occurrence. 



The two points of interest offered by the specimens here described 

 are, 1. The crystallization of serpentine, as shown by its optical 

 character ; 2. The direct alteration of the feldspar and mica of 

 graphic granite into the magnesian minerals, deweylite and ser- 

 pentine, while the quartz has been fractured. 



Contraction of Vegetable Tissue.^ Under Frost At tlie last 



meeting of the Botanical Section, Mr. Meehan referred to a 

 prevalent opinion that the liquid in vegetable tissues congeah d 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 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)^ of 3 feet IH 

 inches round, 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 ease of forest trees in iiigh northern 

 regions, may result from the freezing of liquid in the centre 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 Opvntia Rafineaqui and 0. Missouriensis^ shrink remark- 

 ably with the lowering of the temperature. As soon as the ther- 

 mometer 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 Bajinesgui, 

 which in November measured 4 inches in length, is but ;H now, 

 and is not half the thickness it was in the autumn. In the winter 

 when the thermometer was down to 10° above zero, the pen-knife 

 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. MamWaria Nidtnllii, and M. riripora^ with 

 Echinocartus Simpsoni, a mamillose form, drew the mamnifc 

 upwards, and had them appressed as closely as the spines would 

 allow — and some species of Sempervivum did the same. This 

 could only be accomplished by the contraction of the main axis 

 from the apex downwards. Sediim Hisponiciim, which has not a 

 succulent axis, contracts its leaves into longitudinal wrinkles, pre- 



