NOTES ON CONTINENTAL FORESTRY. 1 67 



1. The growth of roots is not continuous throughout the year, 

 but is interrupted by periods of rest, which do not, however, 

 correspond exactly with those of the aerial portions (crowns). 



2. Among conifers, root-vegetation is entirely suspended from 

 November till March or April ; whereas among broad-leaved 

 trees there is no such total interruption, and their roots can 

 develop even in the middle of winter if the season be mild, 

 whereas the month of February and the beginning of March are 

 the times least favourable for root-growth. The decrease in soil- 

 temperature causes the diminution of growth during winter, and 

 its total cessation among conifers is doubtless a natural adapta- 

 tion to severe climates, which has become a hereditary property. 



Here we have a further explanation of why it is preferable 

 to plant broad-leaved kinds of trees in autumn, and conifers 

 in spring. 



3. The roots of most kinds of trees (except larch and alder) 

 begin to grow at a lower temperature than is needed for the 

 commencement of vegetation in the aerial portions (twigs and 

 leaves). This is of course easily intelligible, just as in the same 

 way it is self-evident that a pump or a boiler must first begin to 

 work before any machinery dependent on it can commence opera- 

 tions. The length of time by which root-activity must precede 

 active vegetation in the buds is usually several weeks, though 

 in some cases it is only several days ; but in the case of larch 

 and alder — the former a tree of the higher Alpine tracts, and the 

 latter a tree of the far north and of frost-bound marshes — the 

 buds open about a month before the roots resume their activity. 



That means, of course, that in the meanwhile the buds and 

 young leaves live and develop by drawing on the reserve nutrients 

 stored up in the twigs and branches. And it also at once 

 suggests a partial explanation concerning the deciduous foliage 

 of the larch, because, if its leaves were persistent like those of 

 pines and firs, then any considerable amount of transpiration, 

 through the foliage, before the root-system could supply the 

 necessary water, would inevitably result in the death of the 

 plant — as often happens with the evergreen conifers during 

 bright sunny weather in winter, which induces transpiration 

 while water is not obtainable from the inert roots and frost- 

 bound soil. 



4. During summer, when the soil is driest, the root-growth 

 is interrupted for about three to eight weeks in August and 



