Minnesota Plant Life. 511 



waves rising 1 and falling through the whole period in which the 

 sea existed. Even an ocean, however, as taught by geological 

 science, may disappear; and in the same manner many species, 

 after existing perhaps for thousands of years, have become 

 extinct. Schopenhauer beautifully illustrates this thought by 

 his figure of the waterfall, in which he compares the lions of the 

 desert to the drops of water that hurry to the brink of a 

 cataract, are poised there for a moment, and then plunge into 

 the abyss below. The lion species continues, like the fall, and 

 the lion quality persists just as the rainbow crowns the spray 

 so long as water flows and rocks are strong. 



Reproduction in its broad sense may, therefore, be defined 

 as that form of growth in which a species bridges the gap from 

 individual to individual. It is not a process by which new 

 organisms are created, but one by which the immortal and un- 

 derlying living substance may keep intact the chain of individ- 

 ual bodies that constitutes the species. 



Propagation. It is customary to classify reproductive phe- 

 nomena as propagative and as reproductive in the narrower sense. 

 Propagation is a term applied to all processes by which new 

 individuals come into existence through divisions of the parent 

 body other than in the formation of special reproductive cells. 

 Thus the growth of new potato plants from the bud's or "eyes" 

 on the tubers, the multiplication of house-plants or trees by cut- 

 tings, buds or grafts, the development of blackberries from 

 bent-over canes, of strawberries from runners, of onions from 

 aerial bulbs, are all classified as forms of propagation. Such 

 processes are indicative of strong regenerative pow r er in plants, 

 but it should be noticed that considerable difference exists 

 among different plants in their ability to propagate. Some, 

 like the willows, propagate very easily, others, like the castor- 

 oil plant, with difficulty. Propagative or regenerative power 

 may exist in most of the vegetative organs, and sometimes in 

 true reproductive areas like spore-cases, spermaries or egg- 

 organs, (ienerally speaking, however, propagation is a func- 

 tion of the vegetative tract and is most common in the least 

 specialized portions. Roots and stems, for example, much 

 more frequently give rise to new individuals than do leaves, 

 flower-stalks, petals or seed-coats. In some groups of plants, 



