NURSES 107 



of the same insect. And there is no doubt that the Larch 

 aphis is an aid to the infection of the Larch Disease. 



Larch and Scots Pine is also a bad mixture, except as 

 previously mentioned ; for the Scots Pine will all be of bad 

 quality. Also the fungus of Larch Disease 1 lives as a 

 saprophyte on the bark of Scots Pine. 



The foregoing are, of course, only a few of the many 

 possible mixtures. But they serve to illustrate the difficulty 

 of achieving success when planting species alternately or by 

 alternate rows. 



However, as already stated, the plan of having a row of 

 nurses here and there is quite correct when necessary ; but 

 these rows must not be too close together if an even-aged 

 mixture is being planted. The nurses usually employed are 

 Larch, Corsican Pine, and Scots Pine, which are quick- 

 growing, cheap, and hardy. 



Birch, however, should usually be planted for nurses, as 

 they grow quickly, are immune to late and early frosts, and 

 their shade is very slight, and they will not have to be 

 removed so early as the Pines. In most cases, the Birch 

 should be given 6 to 8 years' start before the tender species 

 are planted. The function of nurses is merely that of 

 protection from inimical influences. Hence they should 

 always if possible be grown as an overwood and the tender 

 species introduced as a separate crop under the shelter of 

 the nurses ; the latter should be removed when no longer 

 required. No attempt should be made to effect any natural 

 pruning by means of the " nurses " ; for such pruning can 

 only be effected to the detriment of their efficiency as 

 nurses. 



Then again, the Poplars should also, in many cases, be 

 largely used for nurses, especially to trees that will bear 

 shade ; however, artificial pruning will always be necessary. 

 On clay land, Poplars planted every 16 feet apart, the rest of 

 the area being pure Spruce, should give very good results ; 

 or if the land be not too stiff and it be desired to grow Silver 

 Fir, the Poplars may be given a few years' start, say 6 or 

 1 According to some authorities. 



