THE METABOLISM OF PLANTS. 



293 



oxygen has access to it. With regard to the higher Fungi 

 Brefeld has observed that though Mucor Mucedo and stolonifer, 

 Penicillium 'crustaceum and others, can live in the absence of 

 oxygen, they do not grow, because they can excite only com- 

 paratively feeble alcoholic fermentation. Mucor racemosus, 

 on the other hand, excites active alcoholic fermentation, and 

 accordingly it can grow in the absence of oxygen. 



We have already learned (p. 203) that temperature has an 

 important influence upon metabolism, and we shall find, in 

 harmony with this, that it materially affects growth. In dis- 

 cussing, in the previous lecture, the general relations between 

 temperature and the metabolic processes, we found that there 

 are three cardinal points to be noted ; the minimum tempera- 

 ture at which the process first begins, the optimum at which it 

 is most active, the maximum at which it ceases. These points 

 we have also to note in considering the relations between 

 temperature and growth. 



The following tables illustrate the relation of growth to temperature. 

 In the first table are given the results obtained by Koppen and de Vries 

 which illustrate the relation in a detailed manner. The measurements 

 refer to increments in length of hypocotyls in periods of 48 hours. 



