STORAGE OF CALORIFIC MATERIAL 427 



much as 49-5 C. Again, in a series of experiments performed by 

 Kraus upon male cones of Ceratozamia longifolia, the highest tempera- 

 ture noted was 38 - 5C, and the greatest excess over the temperature 

 of the surrounding air, 11"7C. The inflorescences of Palms and 

 the flowers of Nymphaeaceae show a similar behaviour. 



The metabolic changes correlated with such a pronounced rise of 

 temperature, have been most thoroughly investigated in the case of 

 Arum italicum by Kraus. The spadix of this plant is prolonged into 

 a massive club-shaped appendage of a golden yellow colour, which 

 protrudes from the cavity of the spathe for some distance. This 

 appendage constitutes the calorific organ. It consists of a cylindrical 

 core of water-tissue, traversed by vascular bundles and surrounded by 

 a wide parenchymatous sheath, which is composed of a number of layers 

 of thin-walled isodiametric cells containing large quantities of starch. 

 In this peripheral parenchyma is deposited the store of respiratory 

 material, consisting of numerous compound starch grains, together 

 with a certain amount of sugar. Before the flowering period begins, 

 carbohydrate substance makes up 77'8 per cent, of the total dry 

 weight of the appendage, 66 per cent, being represented by starch, and 

 12 per cent, by sugars. In the course of the few hours during which 

 the heating effect is noticeable, the dry weight of the appendage 

 diminishes on an average by 74T per cent. This striking loss of weight 

 is accompanied by the entire disappearance of the reserve carbo- 

 hydrates ; these substances are used up in respiration, except for a 

 small fraction (3*7 per cent.), which is transformed into organic acids 

 and other compounds that remain in the tissues of the appendage. 

 The disappearance of the respiratory starch does not take place in any 

 regular basipetal or centripetal sequence. On the contrary, the 

 depletion of the storage-tissues follows a very irregular course in the 

 present instance, patches, strips, and isolated spots retaining their starchy 

 contents at a time when the intervening areas are already emptied 

 of their reserve-material ; ultimately, however, the entire storage-tissue 

 becomes thoroughly depleted. 



Both Kraus and Delpino regard the remarkable production of heat 

 that takes place in the spadices of Aroideae, and in certain other 

 inflorescences and flowers, as an ecological device which serves to 

 attract pollinating insects. There can be no doubt that insects will 

 be attracted to any plant which affords such an exceptionally warm 

 habitation ; the attraction will be greatest towards evening and in the 

 early morning hours, when the difference of temperature between the 

 flower and the outer air is most pronounced. 



