394 PROTECTION AGAINST PLANTS. 



surprisiiifjly short time. Tlius, foxgloves and groundsel on 

 sandsto;ie rock ; balsams and willow-herbs on basalt ; brooms 

 and genista on sandy soils — spring up in masses after a 

 felling. This can be explained only by a supposition that 

 the seeds of these weeds remain dormant in the soil, and 

 germinate only when the removal of the trees allows enough 

 heat and air to reach them.* Jhuming, or the thorough 

 burning of branch wood on the soil, after a clear-felling, may 

 destroy seeds of weeds in the upper layers of the soil, and 

 thus keep it free from w^eeds until it has been restocked with 

 forest growth. 



iii. Age of Wood. 



Forest trees are most endangered by weeds in the first few 

 years of their life. Forest nurseries and cultivations, there- 

 fore, suffer most of all, and of these, sowings and natural 

 regeneration-areas more than plantings. Where weeds 

 abound, very small transplants should not be used, and 

 frequently four or five-year-old plants are preferable. 



Some poles and coppice-shoots, and especially osier-willows, 

 are attacked and frequently killed by climbers and parasites. 



In tropical countries, trees of all ages are liable to be killed 

 by the strong woody climbers and twiners (lianes) which 

 abound in the forests of these regions and attain several 

 feet in girth. These lianes may mount to the top of the 

 highest trees, depriving their crowns of light and bending 

 down and breaking poles with their w^eight. The twiners also 

 constrict trees, moulding their stems into corkscrew shapes, 

 and in the case of trees wath a sapwood, the passage of sap 

 may be so interfered with, that the trees are killed. 



iv. Locality. 

 Fertile, fresh, and moist soils, especially on basalt, produce 

 more weeds than soils over dry sandstone rock. Damp air 

 also favours the growth of weeds, as can be seen from the 

 vigorous weedy growth on mountains. Fortunately, on good 

 soils, the growth of forest trees also enables them to get out of 

 the reach of the weeds sooner than in unfavourable localities. 



* " Cultiiiversuclie mit luhenden samen." C'eiitiallblatt f.d. gcs. Foislwcsen, 

 1S'.)4, p. 138. 



