SCIENTIFIC SUMMARY. 
195 
leaflets do not increase, but they soon begin to enlarge, and by the time the 
surface of the water is reached, they exceed in size the ordinary leaves, 
forming a four-rayed star on the surface. While the petioles of the ordi- 
nary leaves are stiff, so that they stand erect out of the water, these floating 
leaves are weak and flexible, like those of water-lilies, allowing the leaf 
to maintain its position on the surface with the rise and fall of the 
water. Their upper surface is shining and coated with wax, so that the 
water flows off them. If immersed in deeper water, the petioles will 
lengthen still further, even to the extent of three feet. In these cases the 
formation of the organs of fructification appears to be suppressed. In the 
ordinary aerial leaves, stomata are found on both sides of the leaf in about 
equal numbers ; in the floating leaves, on the other hand, the under side is 
entirely destitute of stomata, while on the upper surface they are about 
three times as numerous as in the a&rial'leaves ; thus resembling Nymphcea, 
Hydrocharis , and other plants. 
Icicles in the cells of Plants. — At a meeting of the Academy of Sciences of 
Paris, on 21st February, M. Prillieux sent in an interesting paper on the 
congelation of plants. He has established the existence normally of large 
icicles in the interior of all frozen plants. These icicles form small columns, 
perpendicular to the surface, and often penetrating the epidermis. The ice 
is formed from liquids derived'from the ■cells. The cells themselves remain 
intact, so that there is no destruction, but simply a separation of organs, 
and therefore what has been said concerning the death of plants by freezing 
goes for nothing. 
The Acrogens of Lake Superior , America. — Mr. Macouri, of Belleville, 
lately returned from a somewhat extended botanical tour around the north 
shore of Lake Superior, which occupied him during July and part of August. 
By dint of excessive work, he has made a large collection, many of his 
specimens being of great rarity and interest. A catalogue of all the plants 
noticed and collected by him is in progress, and will probably be published 
by instalments in the Canadian Naturalist. The Acrogens, being worked up, 
are given as a beginning in the last number of that Journal, and the op- 
portunity to include the species obtained by other collectors, in the same 
locality, is availed of. 
Geography of Pinus Pungens. — In a note to a paper on 11 Variations in 
Pinus and Taxodiumf recently published by the Philadelphia Academy of 
Natural Sciences, Mr. T. Meehan has given another locality for them : “ on 
the hills north of Harrisburg, along the Susquehanna,” and he states that 
they are probably abundant through the centre of the State. 
The Colouring Matter of the Alder. — Dingler’s Polytechnisches Journal , 
in its second number for January, gives a paper on this subject by Herrn 
Dreykorn Beichardt, which is thus given in abstract in the valuable 
scientific summary of the Chemical News : — It is a well-known fact that 
the wood of the Alnus glutinosa , L., when recently cut, exhibits a series of 
colourations, rapidly changing from yellow to reddish-brown. The authors 
isolated this colouring matter, which is perfectly insoluble in ether, benzol, 
and sulphide of carbon, difficultly soluble in absolute alcohol and boiling 
water, but readily soluble in dilute alcohol in every proportion. The 
different tests applied to this substance resulted in defining it as a peculiar 
