THE PI.ANT WORLD 155 



great extremes of heat and cold as well as drought without injury. 

 When the plants are taken indoors the necessity of a resting period on 

 account of unfavorable conditions no longer exists, but the habit has 

 become firmly fixed and can not easily be overcome. Nature makes 

 extensive preparations for this time, as we shall see. The seeds of plants 

 are also like ' ' resting spores " in a way, and they rarely grow if planted as 

 soon as they are ripe, but must be kept for some time. When the spring 

 returns the conditions of growth are usually so favorable that it takes 

 place with great rapidity, the result being a struggle for existence 

 between the different species and individuals as well. Anything that 

 will give it the slightest advantage over its fellows may decide whether a 

 plant will survive or not. It is obvious that a good start at the begin- 

 ning of the growing season is of importance. At that time there are no 

 green leaves, unless the plant is an evergreen, to manufacture food 

 material from the carbon dioxide of the air and the substances taken in 

 through the roots ; and unless the plant has some reserve food left over 

 from the previous summer it is not easy to see just how it would get along. 

 Accordingly, we find that most plants spend a large part of the growing 

 season in laying up a supply of starch in the stems or roots, just as a 

 similar food supply is found in nearly all seeds. Sugar, starch, cellulose, 

 and gums are closely related chemically, and they are all composed of 

 the three elements — carbon, hydrogen, and oxygen. It is a comparatively 

 easy matter for the chemist to transform the more complex of these com- 

 pounds into the simpler ones, though no one has succeeded in bringing 

 about the opposite change. The plant takes these simpler compounds and 

 from them manufactures the more complex ones, such as cane sugar, gums, 

 starch, and cellulose, which is the ground work of all plants. The most the 

 chemist can do is to break these down into relatively simple substances. 

 Thus, by boiling starch or cotton, which is nearly pure cellulose, with 

 acids we get glucose, etc. So that it is literally true that "sugar can be 

 made from old rags." What we get is not simply something that is 

 sweet like sugar, but it is true sugar. 



The carbon which is contained in starch is obtained from the carbon 

 dioxide ("carbonic acid ") of the air. The hydrogen and oxygen come 

 from the water taken up by the roots. By very roundabout methods the 

 chemist has been able to take these elements and from them has made 

 different sugars, an operation that is carried on by nearly all plants whenever 

 the sun is shining. In the plants the simple sugars are transformed into 

 the more complex substance, starch, which is deposited in certain parts 

 of the organism. In some plants it is stored up in the roots or tubers, 

 or it may be packed away in the stems or elsewhere. In this form the 

 reserve food is useless to the plant, for starch is insoluble and can not be 

 carried to those parts of the plant where it is needed. It must be changed 



