THE PHYSIOLOGY OF PLANT-LIFE 17 



no further change. The number of substances thus 

 formed is enormous, for, as already stated, every plant 

 has its own way of carrying on, the work of decomposi- 

 tion. We may classify them into four great groups: — 



1. The Waste-products. These are of no further use 



to the plant, and are usually packed away in 

 some form in which they will be out of the way. 

 If they constitute a source of danger, they are 

 first of all transformed into harmless substances. 



2. The Reserve products. These are intended to be 



used up as food on a future occasion. 



3. End-products of definite use to the plant. These 



undergo iio further change, but, unlike the waste- 

 products, the plant is benefited by their presence, 



4. Intermediate products of metabolism. 



For our purpose the waste- and other end-products 



are of chief interest. 



Among the vegetable waste - products there occur 



numerous crystalline — and a few liquid — basic, nitro- 



t5 



uloids 



session of very strong physiological action. Morphine 

 was the first of these to be extracted; then followed the 

 extraction of strychnine, brucine, quinine, kc. At 

 present the number of alkaloids isolated and experi- 

 mented with is very large, and chemists are, legitimately, 

 very proud of having been able to accomplish the arti- 

 ficial production of some of them. The alkaloids vary 

 considerably in nature: they are all poisonous, but small 

 doses of a poison under certain circumstances become 

 medicinal. Some plants containing alkaloids are there- 

 fore reo^arded as medicinal because a certain use has been 

 found for their alkaloids; those that contain alkaloids 

 for which no use has been found are merely poisonous 

 plants. The difference is one of degree, not of kind. 



