78 POPULAR SCIENCE MONTHLY. 



substances from one portion of the vegetative tract to another 

 along conduits which lie near the surface. On such compounds, 

 as well as on chlorophyll, the blue- violet rays (see Fig. 2) exercise 

 a disintegrating effect. In quite a large number of plants, the 

 lines of vessels in stalks, midribs, and petioles of leaves are 

 shielded from the direct action of such rays by means of external 

 layers or bands of anthocyan, of some shade of red or purple. It 

 is possible in some instances to trace the line of the conducting 

 vessels by the lines of color appearing near the surface. The 

 direct connection between the food substances and the presence 

 of the coloring matter is strongly indicated by the example de- 

 tailed by Kerner, in which the pearly- white rhizome of Dentaria 

 when taken from the soil and exposed to the light will become a 

 deep violet in a few hours. Whether the connection is a direct 

 one or not, it is also true that many young and rapidly growing 

 shoots exhibit marked reddish or violet colors at a time when 

 reserve food is being conveyed to them in greatest quantity, and 

 when the thin, tender tissues are otherwise so translucent as to 

 allow the sun's rays to strike through them in a manner calcu- 

 lated to work great damage in the complex compounds in the 

 young leaves. When the leaves mature and are not so pervious 

 to light, the colors may disappear. This is well illustrated by the 

 behavior of the young leaves of rhubarb, cherry, and grape. 

 Many instances of this character are known, as well as the fact 

 that storage organs are often provided with coloring layers or 

 shields, when partially exposed to the light under normal con- 

 ditions. In plants with deciduous leaves, or the shoots which die 

 down to the root stock each year, it is highly important that the 

 material in the protoplasmic structures of the portion dying away 

 should not be entirely lost, as it represents a large outlay of en- 

 ergy. As a matter of fact, in plants of this character the proto- 

 plasm, chlorophyll, and other nitrogenous substances are usually 

 broken down and begin to be gradually withdrawn into the sur- 

 viving portion of the plant about the time of the formation of the 

 first stages of the absciss layer which finally cuts off the leaf 

 stalk, or about the time the activity of the herbaceous shoot be- 

 gins to slow down. The disintegration of the chlorophyll would 

 leave the leaf almost colorless and translucent, and the sun's rays 

 would strike directly through it, resulting in the total decompo- 

 sition of the proteids and a consequent waste to the plant, but 

 during the decomposition of the chlorophyll there occurs, as a 

 result or accompaniment of the process, the formation of much 

 brilliant coloring matter of various shades, to which are due the 

 brilliant autumnal tints of deciduous leaves. These coloring mat- 

 ters sustain the same general relation to sunlight as the other 

 colors described above. They generally absorb the entire violet 



