ioo PLANT PHYSIOLOGY. 



is usually inv'estigated principally by water-culture. Answer 

 from your various sources of information. It is important to 

 note what minerals are absorbed and what use is made of them. 



\Yater-culture, especially for its demonstration of the particular role 

 of each mineral in the plant, is a very important subject; but I do not 

 find it profitable for use in such a course as this. Probably it could be 

 managed best by assigning it to some student as a special topic. The 

 students gain some knowledge of its possibilities in their Experiment 13 

 earlier. Full directions are given by Darwin and Acton, and by Detmer. 

 One of the Errera & Laurent diagrams (No. i) gives a very effective 

 representation of results of such cultures. 



It would be profitable here to introduce experimentation upon the 

 amount of mineral matters contained in an ordinary plant. The usual 

 method is to weigh a shoot, dry it out completely in a water-bath, weigh 

 again, burn it to ashes, and weigh the ash. For the precautions and 

 details of manipulation, see Detmer, 80. 



D. Metabolism, (c ) Formation of Special Substances, together 

 TI'//// Storage, Secretion, and Excretion. 



62. What are the principal groups of special substances made 

 by plants? 



Experiment upon this subject is not profitable here ; answer 

 from your various sources of information. The substances 



* 



should be tabulated to show their composition, origin, use, and 

 mode of occurrence. 



This subject, i.e., Plant metabolism, is treated as to its practical ex- 

 perimental study with great fulness by Darwin and Acton. Some phases 

 of it are very easy of experiment, especially to those with some experi- 

 ence in chemistry. 



63. What processes are involved in storage, secretion, and ex- 

 cretion? 



What ecological phases and results are connected with these 



processes? 



No experiment upon this subject is here practicable. 

 Answer from your own observation and your other sources of 

 information. 



The terms secretion and excretion are not usually differentiated in 

 their use. It seems best to apply secretion to cases in which the prod- 

 uct has some use, and excretion to those in which it has no further use, 



