Botany. 77 



The illustrations and typographical execution leave nothing 

 to be desired. <-. u <;. 



•_'. Oh t/n qff\ cts product d on sorru tropical plants by a U mpera~ 

 tun of K) to 84 degrees,* — In horticultural language, a stove is a 

 hot-house, specially adapted for the cultivation of tropical plants. 

 The temperature at which it is kept, varies, of course, widely, 

 according to the season, but its range in winter is generally from 

 or 60° Falir. at night, to 70°, Fahr. in the daytime. Iii a well 

 regulated establishment, the temperature is not allowed to fall 

 below the minimum just mentioned. If, through accident or 

 neglect, the temperature descends below 45° but is still above 

 freezing, certain plants soon exhibit sinus of having sustained 

 injury. In the case of some of the Crotons, plants cultivated for 

 their foliage, the injury is shown in the partial withering and 

 subsequent fall of the leaves : in the instance of Eucharis, a 

 diminished quantity of flowers is the most obvious result. The 

 temperature at which these injuries are produced may be con- 

 siderably above that of the freezing point of water, and therefore 

 the question of frost is to be left out of account. If the plants 

 were in the open air, the question of frost might well come in, for 

 if a plant is exposed to the open air, on a clear night, when the 

 sheltered thermometer marks a temperature of say 45°, the radia- 

 tion may carry the temperature of the plant even below 32°. In 

 ven house, this reduction of temperature by radiation is prac- 

 tically impossible, and can be left out of consideration. Hence 

 we have to study only the effects produced by the temperature 

 which is indicated by a thermometer close by the plant. 



In order to approach the question as part of a larger inquiry 

 which I have had for some years under investigation, it was 

 thought best that the tissues of certain tropical plants should be 

 examined microscopically, under varying conditions of heat and 

 cold. In the present communication, the principal results of this 

 examination between the somewhat arbitrary limits of 40° and 

 34° will be briefly detailed. 39° is said to be the point at which 

 water reaches its greatest density, while 34° was considered by 

 me to be well within the danger limit so far as frost is concerned. 

 First, as regards the effect on the cell-wall in all the cases observed : 

 there was no physical injury apparent. Second, as regards the 

 effect on the protoplasmic contents : there was merely a reduction 

 of rate of circulation. Third, there was no appreciable change 

 in the size of the sap-cavities, (vacuoles). Fourth, there was a 

 notable reduction of the power of plasmolytic agents, such as 

 Potassium nitrate, solution of cane sugar, etc. This pointed 

 plainly to a diminution in the power of absorption. 



It is well known that the temperature of the soil has a marked 

 influence on the absorption of liquids by the roots, cold diminish- 

 ing the rate of absorption. Comparative experiments now in 

 progress indicate that in this respect tropical plants are even more 

 sensitive than subtropical, and much more so than those of temper- 



* Read Nov., 1889, before American Academy. 



