20 GENERAL HISTORICAL SUMMARY. 



cessive modifications of the deciduous forests of the Harz in connection with 

 their disappearance before the conifers. He showed that the forests remained 

 unchanged just as long as they were undisturbed by man, and that, while 

 trees with winged migrules readily invaded wind-throw areas, they were 

 gradually replaced by the species of the surrounding forest. Humboldt (1850 : 

 10) dealt with succession only incidentally, though he clearly recognized it as 

 universal : 



"In northern regions, the absence of plants is compensated for by the 

 covering of Baomyces roseus, Cenomyce rangiferinus, Leddea muscorum, 

 L. icmadophila and other cryptogamia, which are spread over the earth and 

 may be said to prepare the way for the growth of grasses and other herbaceous 

 plants. In the tropical world, some few oily plants supply the place of the 

 lowly lichen." (125) "Thus one organic tissue rises, Me strata, over the 

 other, and as the human race in its development must pass through definite 

 stages of civilization, so also is the gradual distribution of plants dependent 

 upon definite physical laws. In spots where lofty forest trees now rear their 

 towering summits, the sole covering of the barren rock was once the tender 

 lichen; the long and immeasurable interval was filled up by the growth of 

 grasses, herbaceous plants, and shrubs." 



Henfrey (1852: 56) considered briefly the changes in vegetation due to man: 



"It is certain that the appropriate stations of many plants would be destroyed 

 with the removal of forests, and new conditions of soil created for the habita- 

 tion of immigrants from other regions. But the modification of the surface 

 so as to alter the physical condition of the soU is by far the most important 

 change brought about in reclaiming land for cultivation. The banking out 

 of the sea changes by degrees the vegetation of its shores; bare sand-dunes, 

 where scarcely a plant could maintain a precarious footing, are by degrees 

 covered with vegetation; sandy inland wastes are rescued from the heath 

 and furze, and made to contribute at first by coniferous woods, such as the 

 larch, and when the soil has become by degrees enriched, by the plants requir- 

 ing a better nourishment, to the general stock of wealth; and in these changes 

 many species are destroyed, while others naturally making their way into a 

 fitting station, or brought designedly by the hand of man, grow up and dis- 

 place the original inhabitants." 



De Candolle (1855: 472) cited the conclusions of Dureau de la Malle (1825), 

 Laurent (1849), and Meugy (1850) as to the "alternation of forest essences," 

 a subject much discussed in the works on forestry of this time. He failed, 

 however, to recognize the fundamental nature of succession, for he regarded 

 the alternation (succession) of forest dominants as a process distinct from that 

 which occurs when a forest is burned or cut. It seems probable that the 

 difference he had in mind is that which distinguishes primary from secondary 

 succession. Hoffmann (1856:189) found Rubus to be the first invader in 

 forest burns in the Ural Mountains; this was followed successively by Amelan- 

 chier, Alnus, Betula, and other deciduous trees, and these were finally replaced 

 by pines and other conifers. Hill (1858) first pointed out that the second 

 growth in forest burns or cuttings is normally composed of genera different 

 from those found in the original vegetation. Stossner (1859) described in 

 detail the conversion of a fallow field covered with Viola into a mountain 

 meadow. 



