EXECnTION OP MIXED SOWINGS. 279 



the crowns of the surviving seedlings, there it is necessary to 

 introduce new seedlings. This may be done either by sowing seed 

 again according to any of the methods already described, or by 

 means of planting. When to sow and when to plant vrill be ex- 

 plained in Chapter VI ; but it may be laid down as a general 

 rule that, if no change of species is contemplated, seed will usually 

 be sown to replace yearlings and even seedlings up to two years old- 



SECTION VII. 

 Execation of mixed sowings. 



In describing the use of the sowing porcupine (p. 267) allusion 

 has already been made to the sowing of more than a single species. 

 It may be necessary to sow more than one species either because 

 it is advantageous to grow a mixed forest, or because the species 

 required is so delicate or so slow-grovning as to reqmre to be raised 

 ■with nurses. 



If they are to be sown broadcast, the seeds of the several species 

 must be mixed together in the right proportions. Otherwise it is 

 only when the single species to be permanently maintained is ex- 

 tremely delicate or shade-enduring, or the locality to be sown is 

 exposed to very severe weather influences, or the habits and re- 

 quirements of the several species are unknown 'and have to be 

 ascertained at all cost, that the seeds may be thus mixed together ; 

 and in all other cases the different species should be sown in sepa- 

 rate Knes, the following advantages being thereby secured : 



(i) The different species are never in each other's way. 



(ii) Supervision is at all times easy. 



(iii) In repairing casualties there is never any doubt as to what 

 species to sow or plant, and where and in what abundance. 



(iv) Cleanings and thinnings (to be treated of in Part III) 

 become singularly simple operations. 



(v) As a consequence of the preceding advantages the main- 

 tenance of the mixture, in the correct proportions according to the 

 age of the crop, can never present any difficulty. 



