660 ESTIMATION OF THE HEAT NECESSARY TO GROWTH. 



Constants for the Commencejvient of Leaf-fall. 



Bird Cherry (Prunus Padus) 6179°. 



Small-leaved Lime {TUia parvifolia) 6644°. 



Elder {Sambueus nigra) 6644°. 



Alpine Woodbine {Lonicera alpigend) 6759°. 



Pear (Pirus communis) 6788°. 



Walnut {Juglans regia) 6816°. 



Trumpet-tree {Catalpa syringoefolia) 6816°. 



Violet Willow {Salix daphnoides) 6838°. 



Horse Chestnut {^Esculus Hippocastanum) 6863° 



Hazel {Corylus Avellana) 6884°. 

 Gooseberry {Ribes Grossularia) 6884"*. 

 Beech (Fagus silvatica) 6884°. 

 Vine ( Vitis vinifera) 6913°. 

 Oak {Quercus pedunculata) 6979°. 

 Apple {Pirus Malus) 6999°. 

 Chestnut (Casianea sativa) 7023°. 

 Gean {Prunus avium) 7023°. 

 Plane {Platanus acerifolia) 7145°. 



Although the computations which have been made at different places and over 

 several years, by way of trial, have given figures which do not differ materially 

 from the above, and it seems as if these constants actually justified that term, yet 

 confidence in them has been to some extent diminished by the following considera- 

 tions. 



With regard to the germination of seeds it is concluded from various phenomena 

 that the heat liberated in respiration from the cells, as well as the temperature of 

 the soil, has not a little influence also on the process of growth. Seeds in whose 

 cells the protoplasm has once been set in action by an external impulse, perhaps by 

 a minimum of radiated or conducted heat, respire with a fair amount of activity. 

 In this way the reserve materials stored up in them are consumed, and so much 

 heat is liberated that not only is the embryo able to develop, but heat may be 

 even given up to the environment. Radicles of germinating maple and wheat 

 seeds, which by chance were found in an ice cellar, were observed to grow down 

 into the blocks of ice, and this could only have happened from the melting of the 

 ice by the radicles, which push their way into the cavities formed, like the flower- 

 buds of the Soldanellas already described. In many cases of observed germina- 

 tion it may therefore be doubted whether the growth of the embryo alone is to 

 be laid to the account of the measured heat, supplied to the seeds from their sur- 

 roundings. On the other hand, it is doubtful whether the heat (registered by the 

 thermometer), which reaches the plants from outside, is employed only in growth. 

 One part may be used in order to maintain the plant-organ in question alive; 

 another portion may be useful in the production, and in the transformation and 

 transmission of constructive materials, and only a residual portion can then partici- 

 pate in growth. But this is not all. It is also doubtful whether the positive heat 

 entering the plants from outside, can be always completely disposed of, within 

 the given space of time, in the various chemical transformations and molecular 

 arrangements carried on in the interior of the plant, and whether an unused 

 surplus is not sometimes present which should be really withdrawn from the 

 calculation. It is tacitly implied in the reckonings that if the plants are exposed 

 to a constant temperature of 20° for 12 hours, the total heat which was able to 

 raise the mercury up to 20° in that time would also be turned to account by the 

 plants. But that this is not so, is shown by the following observations: 



