PLANT PHTSIOLOGT. 81 



protoplasm of the living tissues, and constitute its most 

 important food. In connection with the nitrates and sul- 

 phates, etc., also imbibed, they furnished the materials for 

 the increase of protoplasmic substance in growing cells. 



143. The Storing of Reserve Material. — In many plants 

 the surplus starch is stored up in one or more organs as re- 

 serve material ; thus in the potato the starch formed in the 

 leaves in sunlight is, in darkness, transformed into glucose, 

 or a substance very nearly like it, and in this soluble form 

 it is diffused throughout the plant, and in the underground 

 stems (tubers) is again transformed into starch. So in the 

 case of many seeds a mass of reserve material is stored up, 

 generally in the form of starch (e.g., the cereal grains), and 

 sometimes in the form of oily matters (e.g., the seeds of 

 mustard, flax, castor-bean, squash, etc.). 



144. The Use of Reserve Material. — In the use of reserve 

 material, as in the germination of starchy seeds, the starch 

 appears to undergo a change much like that in its disap- 

 pearance from chlorophyll. Here it is certain that oxygen 

 is absorbed, and that carbon dioxide is evolved, while the 

 starch is transformed into glucose. Similar transforma- 

 tions doubtless take place in the use of the starch stored up 

 in buds, twigs, stems, bulbs, etc. 



145. In the germination of oily seeds, after the absorp- 

 tion of oxygen, starch is (in many cases, at least) first pro- 

 duced, and from this the soluble sugar is formed. In any 

 case, after the sohition is attained, the subsequent changes 

 are similar to those which follow the transformation of the 

 starch of the chlorophyll. 



146. Alkaloids and Acids. — Among the most obscure of 

 the subsequent chemical changes are those which give rise 



