38 JBotanis 



notice the amount of sap issuing from any cut, we 

 recall what seems an extraordinary fact — that in 

 July and August stems being cut do not leak or 

 bleed, and yet in those summer months that under- 

 ground engine, the root, must be pumping up liquor 

 faster than ever to maintain all that luxuriance of 

 leafy growth. The explanation of this is simple : 

 the plant, when well provided Avith leaves, is 

 devouring for its own nutrition so much sap — " using 

 it U2:> " so fast — and is also losing so much moisture 

 to the air, by reason of transpiration, or giving off 

 of water in vapor, that no matter how hard the root 

 works no water remains standing in the vessels to 

 run out when cut. Here, of course, we except those 

 peculiar, fleshy stems of some plants of arid coun- 

 tries, which stems are always a storehouse of water. 

 In our February walk, when the absence of leaves 

 and of herbage gives good opportunity for the study 

 of woody perennial stems, we at once notice how 

 the shape of these is affected by the circumstances 

 of their 2:)lace of growth. In a thick wood the stems 

 are slender and tall, shooting up in their effort to 

 obtain air and sunlight. When valuable trees are to 

 be cultivated, either as landscape ornaments or as 

 timber supplies, one early j^rocess is to " thin them 

 out, " giving each one room to make a large stem or 

 bole. Travelers in troj^ic lands tell us that in the 



