486 Minnesota Plant Life. 



beo-in again. A strong electric shock stops it forever. This 

 streaming, pelhicid sHme is the Hving substance. 



Not only in hair-cells does the living substance commonly 

 occur, but in many other portions of the plant. It is found 

 at the tips of all young roots and buds. In the green cells of 

 lea\es it is always present. It will be found in certain of the 

 conducting-areas of the plant — in the leaf network and in the 

 young fibers of the stem. In trees and shrubs it occurs neither 

 in the mature bark nor in the mature wood of the trunk, 

 branches or woody roots. Between the bark and wood there 

 exists, however, in ordinary trees a thin layer — no thicker, in- 

 deed, than tissue paper — known as the caiiibiimi. In this layer 

 of cells the living substance will be found. It occurs in all 

 spores, eggs and spermatozoids, in all ver}- }oung organs and 

 tissues, and in general in all growing parts of the plant. 



Physical structure of the living substance. Years ago when 

 investigation of the living substance was in its infancy it used 

 lobe described as a "structureless slime" or as "living jelly" — 

 these phrases indicating how little was really known of its or- 

 ganization. The researches, however, of the last fifteen years 

 in particular, have revealed that the intimate structure of the 

 living substance is extremely complex — so much so. indeed, 

 that a new science, the science of the cell, has developed, until 

 to-day libraries can be collected in this field alone. It would 

 appear that, just as the body of a plant or animal is composed 

 of cells and their products, so the particle of living substance 

 in each active cell is itself composed of smaller bodies and their 

 products, the whole constituting an organism of extreme com- 

 plexity. It may properly be said that there are now known 

 three hierarchies of life — social life, intlixidual lite, and cell 

 life. In the first of these man has his place as a C(ini])oneni 

 bi)d\', in the second he exists as a self-sustained indi\ idual. while 

 in the third lies the living basis of his organi/ation. 



Modern research has shown that the motion seen in a li\ing 

 cell lying under the microscope of the observer is by no means 

 disorderly or unrelated. On the coiUrary the kaleidoscopic 

 changes in the li\ing substance are now known to lia\e pro- 

 found significance in nutrition, growth .and heredity. The dif- 

 ference between the old ide.'i .and the new ni;i\" be siu-vested b\- 



