THE AMERICAN BOTANIST 



25 



Heat Generated by Plants. — Plants are not so warm 

 as animals for the reason that their bodily processes do not pro- 

 ceed so rapidly. In nature, however, there is rarely a mani- 

 festation of energy without the evolution of heat and plants are 

 no exception to this rule. In plant parts that are rapidly de- 

 veloping, respiration is accelerated and a corresponding rise in 

 temperature occurs. The common skunk's cabbage is often 

 cited as an illustration of this. If one measures the temperature 

 within the flower spathe he will find it noticeably higher than 

 the air near by. A recent number of the Kezu Bulletin records 

 some measurements made on the male cones of Enccphalartos 

 Hildcbrajidfii just as they were ripening their pollen, which 

 indicated that they were more than sixteen degrees warmer 

 than the air. The difference is great enough to be perceptible 

 without a thermometer. Several other plants in the cycad 

 family, to which the species just mentioned belongs, are noted 

 for the heat generated at flowering time. Among these are 

 Ccratozainia longifoUa, Cycas circinalis, Macro^amia MiqueUi 

 and Dioon cdulc. It is to the relatives of the skunk's cabbage, 

 however, that the palm must be awarded for differences in this 

 respect. Most of them produce their flowers in sheltering 

 bracts or spathes and afford ideal conditions for measuring the 

 heat. The ceriman of the tropics (Monstera deUciosa) familiar 

 as a large climbing vine in northern conservatories, is reported 

 as having shown a difference of twenty-seven degrees between 

 its flowers and the surrounding air. 



Sources of Nitrogen for Plants. — Although about 

 four-flfths of the air is nitrogen, ordinary plants are unable to 

 use any of it. Nitrogen, however, is an absolutely indispensible 

 element and the efforts of the farmer in fertilizing his land is 

 largely directed to supplying matter that contains it. For a 

 long time it has been assumed that all the nitrogen in plants is 

 taken in through the roots in the form of nitrates, produced 

 from decaying animal and vegetable matter by bacteria. Re- 



