474 AGRICULTURAL REPORT. 



that they have become experts to that degree that they succeed in productng 

 the flower or the matured fruit on a given day. 



"While there can be no doubt that different plants require different amounts 

 of heat from the time of sprouting to full maturity, though the time through 

 ■which this may be furnislicd may be different in different ins^tances, and that a 

 great heat may produce the same effect on plants which is produced by a lower 

 degree operating during a longer term, another principle of much importance 

 must be observed in order to the successful cultivation of plants under natural 

 or artificial circumstances. 



This second principle is that each species requires for each one of its physi- 

 ological functions a certain minimum of temperature, or, as has been well said, 

 each species of vegetable is a kind of thermometer which has its own zero or 

 lowest degree at which it will vegetate. A temperature above a certain mini- 

 mum of heat is found necessary for germination, another for one chemical 

 modification, and a third for flowering, a fourth for the ripening of seeds, a 

 fifth for the elaboration of the saccharine juices, and a sixth for the develop- 

 ment of aroma or bouquet. A certain intensity of light is also demanded to 

 render green the tissues, and a due supply of humidity in the air and in the 

 soil to furnish a vehicle for the materials of growth and prevent undue desic- 

 cation. A plant is thus not only under all the influences which affect the ther- 

 mometer, but is likewise acted upon as is a hygrometer by humidity and 

 dryness. 



From the study of special examples among plants, under the combined in- 

 fluences of temperature, light, and moisture, a later inquirer believes he has 

 reached most interesting results regarding the limiting effects of these causes 

 towards the north, and on mountain sides. From the point of view taken by 

 this later investigator botanical geography ceasee to be a simple accumulation 

 of facts, takes a place among the sciences, and assumes to explain by the study 

 of the distribution of living plants the actual conditions of climate, as well as 

 those that prevailed in former ages. It is to Alphonse de Candolle, who, in 

 his Geographic Botanique Raisonnee, has presented to the scientific public one 

 of the most important works that has of late appeared, and one of the most 

 generally interesting, both on account of the subjects it treats of and the signal 

 ability and thoroughness with which most of them are handled, that we are in- 

 debted for a clearer insight into the obscurity which has shrouded the subject 

 of the geography of plants. " This work," which, in the language of Dr. Asa 

 Gray, " is one that addresses and will greatly interest a much broader circle 

 of scientific readers than any modern production of a botanical author, and 

 which will probably long be esteemed the standard treatise upon a wide class 

 of questions highly and almost equally interesting to the botanist, the zoologist, 

 the geologist, the ethnologist, and the student of general terrestrial physics," is 

 HOt to be found in our bookstores, and appears upon the shelves of only one library 

 in Philadelphia, the magnificent natural history collection of the Academy of 

 Natural Sciences. " Truly we are an enlightened people!" A. de Candolle 

 has proved himself a son worthy to bear the name and continue the renown of 

 his father, Pyramus de Candolle, who Avas the only botanist since Linnaeus that 

 embraced all branches of the study with an equal genius, and whose works 

 mark a new era in the progress of his science. The limits which we have 

 assigned to this paper forbid an extended notice of this work, and we will con- 

 fine our remarks to a few illustrations of the results arrived at, and refer the 

 inquiring reader to Dr. Asa Gray's notice, in Silliman's Journal of Science, 

 vol. XXII, pp. 429, 432, and to Hooker's Journal of Botany, spring and summer 

 of 1856, for a more extended critique. 



