514 THE INFLUENCE OF MUTILATION ON THE FOEM OF PLANTS. 



stigmas of the Bianthus alpinus which had yielded the seeds for the first experi- 

 ment had been pollinated by insects with the pollen of Bianthus deltoides. 



Mistakes often arise also from the fact that the young stages of many plants 

 are very different from the fully-grown specimens. Young Birches grown from the 

 seeds of Betula verrucosa bear leaves which are simply serrated, thickly covered 

 with hairs, and soft to the touch. They are deceptively like the leaves of adult 

 plants of Betula alba or pubescens. The leaves of the adult Betula verrucosa have 

 quite a different form; they are doubly serrated, smooth, and harsh to the touch. 

 These latter are the only form of leaf described in Botanical books for Betula 

 verrucosa. Anyone sowing the seeds from a grown tree, and watching them grow 

 up, with leaves of a different shape and surface, might easily think an actual 

 fundamental change had occurred, and might be tempted to regard the transforma- 

 tion as the direct effect of a change in external influences. 



It is perhaps superfluous to state that due regard was paid to these possible 

 sources of error in the later series of cultural experiments, carried out during six 

 years in the Alpine garden on the Blaser (2195 metres), and for comparison in my 

 Villa Marilaun in the high-lying Tyrolese Gschnitzthal (1215 metres), in the 

 Botanic Garden at Innsbruck (569 metres), and in the Botanic Garden of the Vienna 

 University (180 metres); in no instance was any permanent or hereditary modifi- . 

 cation in form or colour observed. 



Seeds of a plant grown in the valley when sown in the Alpine region produced 

 plants which exhibited the modifications described above. They were also mani- 

 fested by the descendants of these plants but only as long as they grew in the same 

 place as their parents. As soon as the seeds formed in the Alpine region were 

 again sown in the beds of the Innsbruck or Vienna Botanic Gardens the plants 

 raised from them immediately resumed the form and colour usual to that position. 

 The modifications of form and colour produced by change of soil and climate are 

 therefore not retained in the descendants; the characteristics which appear as the 

 expression of these changes are not permanent, and the individuals are to be there- 

 fore regarded as varieties, of which Linnseus says in his PhUosophia Botanica: 

 " Varietates tot sunt, quot differentes plantse ex ejusdem speciei semine sunt pro- 

 ductse. Varietas est Planta mutata a caussa accidentali: Climate, Solo, Galore, 

 Ventis, &c., reducitur itaque in Solo mutato." 



THE INFLUENCE OF MUTILATION ON THE FORM OF PLANTS. 



When Birches and Firs grow up side by side in a wood-clearing, the crowns 

 of the Birches will overtop the Firs in some twenty years' time, and this will 

 seriously interfere with the growth of the latter. With every blast of wind the 

 whip-like branches of the Birch strike against the upper shoots of the Firs, so 

 that these gradually wither and die off. A lateral branch of a Fir tree altering 

 its direction of growth and replacing the dead leader will, in its turn, soon be 

 scourged to death. The top of the Fir is permanently mutilated, and the injury 



