i8o THE PHYSIOLOGY OF PLANTS 



warm saturated atmosphere which would cause the decay of the 

 tips of the Pelargonium. 



Cuttings of the double white Primula can do with a good 

 deal of moisture and of warmth, but they must have a large 

 amount of light. Those who have no bottom heat at their 

 disposal should keep the cuttings fairly dry, and can place 

 them in the open in a fairly shady position. The leaves, it is 

 true, will wither, and the rooting will take a long time, so 

 that a gardener could not use his method with any degree of 

 security. 



No time can be fixed for striking herbaceous cuttings. 

 Shoots may be taken as soon as they have received a certain 

 rigidity and have some fully developed leaves, supposing 

 always that there is still sufficient time favourable to vegetative 

 growth to enable the formation of roots to take place. 



If, however, the season is too far advanced to make success 

 certain, it is better to take fully developed leafless woody 

 shoots for propagating. Besides this kind of woody cutting 

 mentioned, which may be called a winter cutting, in some 

 shrubs not liable to damage by frost autumn cuttings may 

 prove successful. Less hardy genera, too, if they are well 

 protected from the frost, give very good results with autumn 

 cuttings (Roses). 



We may give the following general instructions for the 

 treatment of all cuttings made from dormant wood. 



We want the shoot which we have put into the soil to use 

 its starch and the other stored up food material for the produc- 

 tion of callus and adventitious roots, instead of passing it into 

 the buds, as would have been the case if the branch had been 

 left attached to the plant. The conditions in which the cut- 

 ting is placed are very favourable for such a course ; for on 

 the one hand, the wound caused by the cut, when in contact 

 with the damp soil, acts attractively to the food matter, which 

 has become soluble during the vegetative period. Secondly, 

 one main factor in the expansion of the buds is wanting, and 

 that is the root pressure. The buds of cuttings, therefore, un- 

 fold much later than those of the parent plant. 



These conditions must, therefore, not be disturbed, but 

 should be maintained until the callus covering the cut is able 



