CH. n. 



COURSE OF THE SAP. 



51 



Liebig writes : ' The verdant plants of warm cli- 

 mates are very often sucli as obtain from the soil only 

 a point of attachment^ and are not dependent on it for 

 their growth. How extremely small are the roots of 

 the Cactus, Sedum, and Sempervirum, in proportion to 

 their mass, and to the surface of their leaves ! ' In the 

 next paragraph, he with much naivete refers to experi- 

 ments of Lukas at Munich ; who, by mixing charcoal 

 with the soil^ gives a wonderful growth to 'young 

 tropical plants^' of all descriptions. Among other 

 plants, ' a cactus, planted in a mixture of equal parts of 

 charcoal and earth, throve progressively, and attained 

 double its former size in the space of a few weeks. The 

 use of the charcoal was very advantageous with several 

 of the Bromeliaceas and Liliacese, with the Citrus and 

 Begonia also, and even with the Palmge.' Here the 

 roots must have served as more than ' only a point of 

 attachment,' and the increased growth must have been 

 from the soil, not from the air. 



But, according to Liebig, there's nought like chem- 

 istry. He would do as much with his atmospheric 

 chemistry as the currier with his leather. He generates 

 and feeds his leaves by the carbonic acid of the atmo- 

 sphere ; and when he has done with them, he destroys 

 them with the oxygen of the atmosphere. And he 

 forms his trees by mechanical patchwork, and by 

 juxtaposition, as he would a stalactite, or as he would 

 the trees in the garden of a doll's house. 



• When the food of a plant is in greater quantity 



E 2 



