DEVELOPMENT OF LIGHT AXD HEAT. 501 



shortly before sunrise exhibited a temperature of 10'6 C. when the temperature of 

 the surrounding air was 8'4. On a mountain meadow under a cloudy sky and in 

 calm air the interior of a flower of Campanula barbata showed a temperature of 

 16'6, and not far off' on the borders of a forest the interior of the helmet-shaped 

 sepal of Aconitum paniculatum, 14'6, while the temperature of the outside air in 

 both instances did not exceed 13'2. The temperature of the air in the neighbour- 

 hood of a respiring plant shows a much greater rise if numerous, small, thickly- 

 crowded flowers are inclosed in a common sheath, and especially when the space 

 inclosed is undisturbed. In the same mountain meadow in which the temperature 

 of the interior of the ball in the above-mentioned campanula (Campanula barbata) 

 was tested, the Carline Thistle (Carlina acaulis) was also in full bloom. As the 

 sky was cloudy, the capitula were closed, i.e. the apices of the stiff, involucral leaves 

 were bent together, and formed a hollow inverted cone over the flowers. A ther- 

 mometer placed between these bracts and pushed down as far as the flowers, showed 

 a temperature of 20*4, the temperature of the surrounding air being 13'2, the dif- 

 ference, therefore, was more than 7 C, 



In palms, whose numerous small crowded flowers are covered by large floral 

 sheaths or spathes, the air within these coverings exhibits a rise of temperature 

 which is so noticeable that it can be felt by placing the bare hand inside. The 

 same thing occurs in the aroids. Here numerous small flowers are united into a 

 spike on a thick fleshy axis, forming the so-called spadix, and each spadix is 

 surrounded by a bract which at first is twisted together like a conical paper bag, 

 being often distended like a barrel or inflated like a bladder. It is soon formed 

 into the characteristic shape, but always incloses a cavity whose air is hardly ever 

 disturbed by the influence of other air currents. With care a thermometer may be 

 introduced into this cavity, and the temperature shown by it may be compared 

 with that of the surroundings. For example, it was found when the temperature 

 of the outer air was 25, that in the interior of the spathe of the Brazilian Tomelia 

 fragrans was almost 38. At the same air-temperature the interior of the spathe 

 of Arum cordifolium, in the island of Bourbon, exhibited a temperature of 35-39. 

 But the highest temperature has been noticed in the Italian Arum (Arum Italicum). 

 This plant is very common in the region of the Mediterranean flora, and is fre- 

 quently to be met with in vineyards under bushes, and even in hedges and road- 

 sides. Its spadices, surrounded by large pale-green spathes, push their way in the 

 spring through the soil like inverted conical bags; the spathe begins to open 

 between 4 and 6 o'clock in the afternoon, and at the same time a peculiar fragrance, 

 like wine, becomes noticeable in the neighbourhood of the plant. If a thermometer 

 is introduced into the cavity of this spathe, it is shown that while the temperature 

 of the outside air is about 15, that in the interior has risen to 40, sometimes even 

 to 44. These Aroidese therefore exhibit a temperature in the neighbourhood of 

 their respiring flowers which exceeds that of blood-heat. 



In proportion as the energy of respiration increases with the rising temperature 

 of the surrounding air from morning till afternoon, the temperature in the interior 



