78 Scientific Intelligence. 



ate climates. In the delicately balanced economy of tropical 

 vegetation, even the slight disturbance resulting from carrying 

 the temperature down below the point most favorable for absorp- 

 tion, and yet still considerably above that of the freezing point 

 of water, the supply of water is so much diminished that the 

 withering of the leaves is the natural result. Fifth, Pfeffer has 

 pointed out the interesting fact that although living protoplasm 

 resists the entrance of colored liquids of even moderate strength 

 of solution, it will permit very dilute coloring agents of some 

 kinds to pass into its substance and even to enter the sap cavities. 

 I find that there are not only differences in regard to the absorp- 

 tion of the same liquid at different temperatures, but also of the 

 same liquid by different plants and especially the plants of dif- 

 ferent climates at the same temperature. For the purpose of 

 this later study, it has been found convenient to use the apparatus 

 described by me in a communication read before the Academy 

 two years ago, and which has since that time found elsewhere 

 extended application. 



There is a curious embarrassment attending the selection of 

 material for these studies which I have felt from the outset : Is 

 it not likely that some of the plants cultivated by us in our hot- 

 houses as tropical, and which came originally from the tropics, 

 have become more or less modified through adaptations to their 

 new surroundings ? At any rate, I am not yet prepared to deny 

 that here may be an element of uncertainty when we apply the 

 results of this research to the vegetations of tropical plants in 

 their homes. Again it must not be forgotten that we make little 

 distinction in our hot-houses between those tropical plants which 

 grow in jungles where they may be sheltered more or less from 

 radiation, and those which grow in the moist plains under an open 

 sky. For subjecting the tissues of the plants to varying tempera- 

 tures a special apparatus has been devised by me which forms 

 the subject of a separate communication. g. l. g. 



3. On an Apparatus for easily controlling temperatures at or 

 below freezing, for experiments on the relations of plants to cold* 

 — The ingenious device by which, through the intervention of a 

 refrigerating coil, it is possible to make excavations in sandy and 

 treacherous land, gave the writer a hint as to the construction of 

 a simple instrument for subjecting plants to low temperatures. 

 Expressed in its lowest terms, the apparatus consists of a metal- 

 lic or glass tube running round the inside of a properly arranged 

 box adapted to the reception of a microscope. Through this coil 

 there is made to circulate by means of a pressure bulb, a current 

 of a dense solution of calcium chloride kept at the desired tem- 

 perature. This solution can be carried down far below the freez- 

 ing point of water, and it is of course capable of being kept 

 perfectly under control. In this way, the temperature of the 

 interior of the box falls after a short time to- the desired degree, 

 and it can be kept at this point for any length of time. It is to 



* Read before the American Academy, Nov., 1889. 



