THE SEED 79 



in which micro-organisms were excluded as far as 

 possible, a rise of forty, fifty, and even more degrees 

 above the surrounding temperature has been observed. 

 Apparently this heating process is of advantage to 

 growing seedlings, because numerous observations made 

 by farmers and also more exact experiments by botanists 

 have proved that the rapidity of germination, i.e. of the 

 first appearance of the rootlet and the further growth 

 of the embryo, depends directly upon the temperature ; 

 and, moreover, that for different plants there are 

 different limits at which germination is arrested. For 

 a great number of plants we can determine the lowest 

 and the highest temperatures at which germination will 

 begin ; between these two limits the rapidity of growth 

 increases up to a certain temperature, beyond which it 

 begins to decrease. In this way we distinguish three 

 temperatures : the minimum and the maximum, forming 

 the two limits of possible germination, and then the 

 optimum, at which the process is most successful, i.e. the 

 most rapid. Our cereals, for instance, generally begin 

 to germinate at about 35°-40° Fahrenheit, and the higher 

 the temperature the quicker the development ; but 

 beyond 66°-68° Fahrenheit the process becomes slower 

 again, and almost stops at ioo°. For a long time it was 

 supposed that at 32° F., i.e. at the freezing-point of water, 

 all active life, and consequently germination also, were 

 impossible ; but recently the interesting discovery was 

 made that seeds can germinate even in ice. The experi- 

 ment was as follows : a small cavity was hollowed in a 

 piece of ice, seeds were placed in the hollow and covered 

 with another piece of ice ; the whole block was then 

 placed in a box surrounded with a layer of ice two feet 

 thick. Two batches of seeds were treated in this 

 way, one in January and another in March, and kept in 

 a cellar. Two months afterwards, i.e. in March and 

 May respectively, seeds of the most various plants, 

 such as wheat, rye, beans, cabbage, mustard, were 



