62 Studies in Forestry [CHAP. in. 



twice as great, and that of the Pines as about half as great 

 again as that of Beech, which is the most energetic of the 

 broad-leaved species. It will be seen, from what has previously 

 been said, that the productive energy of the individual tree 

 may be widely different from the productive energy per acre of 

 a pure forest of that species \ and it will therefore readily be 

 intelligible how advantageous alike from the material, the 

 financial, and the sylvicultural points of view the judicious 

 formation of mixed crops may be as compared with pure forests, 

 more especially if formed of the light-demanding species. 



VI. Differences with regard to Reproductive 

 Capacity. 



Trees may reproduce themselves either by means of seed, 

 or else by means of shoots from the stool, or through suckers 

 thrown up from the roots. Reproduction from seed is the 

 normal process of regeneration of all species that are indi- 

 genous, or that have thoroughly naturalized themselves in our 

 climate ; whilst the formation of stoles or root-suckers is princi- 

 pally confined to English Elm, and to exotic Poplars and Willows, 

 which cannot be relied on to form seed of anything like average 

 germinable capacity ; of indigenous trees, Aspen and Willow 

 are the only species endowed with this quality to any great 

 extent. The formation of shoots from the stool is not so much 

 a regenerative measure as rather an effort at recuperation and 

 replacement of the stem or bole when the ascending axis ha ; 

 been removed. It is solely due to the vital activity of the 

 root-system, which, until late in life, remains active after the 

 stem and crown have been removed, and which endeavours, 

 by a new flush of shoots and foliage from the adventitious or 

 dormant buds at the neck of the stump, to obtain the means 

 of assimilating the food that it continues to absorb from the 

 soil. This same tendency is seen in pollarding as well as 

 in coppicing, but in another form and a more limited degree. 



