498 DEVELOPMENT OF LIGHT AND HEAT. 



develop very rapidly to a considerable size, and connected with this rapid growth 

 there is always a rapid movement of the food absorbed by the mycelium, com- 

 bined with an energetic respiration. Respiration is carried on chiefly at the 

 periphery of the receptacle in the mushrooms especially in the hymenial layer, 

 which is very well protected from evaporation and radiation by its position on 

 the lower side of the cap. Transmission of the food, and in particular of a large 

 amount of water, takes place through the stalk which bears the cap. Numerous 

 observations of fungi growing in their natural free condition, and rising but 

 little above the soil, have invariably shown this result: the rise of temperature in 

 the tissue of the cap is most pronounced where respiration is carried on most 

 actively, i.e. in the hymenial layer. It is less in the central portion of the cap, 

 and least in the stalk, through which the watery fluid travels at a temperature 

 which differs but slightly from that of the surrounding earth. Respiration, of 

 course, cannot be considerable here. For example, in Boletus edulis, from its size 

 and shape particularly well suited for these investigations, the following results 

 were obtained while the temperature of the surrounding earth was about 13 C. : 

 temperature of the stalk, 14'2-15*6; temperature of the body of the cap, 15'2-16'8; 

 of the hymenial layer, 16'7-18*1. Further developed (but still quite fresh) fructi- 

 fications exhibit higher temperatures than younger ones which have just appeared 

 above the ground. Observations on other fungi of the Hymenomycetes yield like 

 results. When the temperature of the surrounding earth was 12'2 Lactarius 

 scrobiculatus exhibited in its stalk a temperature of 14'8, and in its cap of 16'0; 

 Agaricus muscarius in its stalk 14*2, and in its cap 15*2, while the temperature 

 of the surrounding soil was 13'0; Hydnum imbricatum, 13'0 in the stalk and 

 14'5 in the cap, while the surrounding earth showed a temperature of 12 '2. The 

 peculiar shape of the cap in these last-named fungi is not well adapted to a 

 separate measurement of the temperature in the body of the cap and in the 

 hymenial layer, but it is probable that a slight difference exists between them, 

 similar to that found in Boletus. The puff-balls belonging to the Gasteromycetes 

 also exhibit a considerable rise of temperature above that of their surroundings 

 in the respiring portions of their fructifications. Thus in Lycoperdon ccelatum a 

 temperature of 15'8 was observed in the spherical receptacle shortly before dehis- 

 cence, while the temperature of the surrounding soil was only 12 '2. 



The liberation of heat appears especially noticeable, too, in respiring flower-buds 

 and in the rapidly-growing stalks which bear them, as well as in opened flowers. 

 If the flowers are small, and if there are but few of them at the end of the stem, 

 or if only a single small flower is borne at the end of a delicate stalk, the heat 

 liberated may easily escape observation; but under very favourable conditions it 

 makes itself readily manifest, and gives rise to a phenomenon so strange and 

 unintelligible that everyone on observing it for the first time is surprised and 

 puzzled. I refer to the fact that small and delicate flowers grow buried beneath 

 the snow, and obtain the space they require by melting the hardened snow. The 

 Alpine Soldanella is a very marked instance in point. As the snow melts and the 



