of Latliraa Squaynaria, i'^c. 41? 



mode of growth, that we must endeavour to find a solution of this 

 problem. 



By laws which almost universally prevail in the vegetable 

 kingdom, plants imbibe moisture from the soil by means of 

 their radical fibres, and gases and moisture from the atmosphere 

 through the medium of pores in the cuticle of their leaves. 

 These elements are conveyed into the parenchyma, where innu- 

 merable and inconceivably delicate organs, stimulated by light 

 and heat, throw off the oxygen and retain the hydrogen and 

 carbon. These essential ingredients at once produce the green 

 colour, and are converted, by a mysterious and hidden process, 

 into the several substances of the vegetable body. Parasitical 

 plants, in one or more respects, and in different ways, are excep- 

 tions to these general laws. Though the Lathrcea, unlike many 

 of its tribe, has leaves amply supplied with absorbents, these 

 organs are doubly concealed in a cold subterranean laboratory, 

 and there destined to breathe in darkness ; while the flowering 

 stem, — the only part in contact with the light, — is destitute of 

 those cuticular pores through which air can be admitted, and by 

 means of which the ordinary functions can be performed. The 

 materials and the stimulus are at hand, but for want of the 

 proper apparatus they cannot act. Again : the radicles of the 

 Lathrcea do not imbibe moisture immediately from the soil, but 

 extract the already assimilated juices of its foster-parent ; and 

 whether we suppose these juices to be derived from the inner 

 cortical layers after the accession of carbon through the leaves, . 

 or from the alburnum, where they are in a less combined state ; 

 they probably contain no free hydrogen to minister to the gene- 

 ration of the green colour. They may also undergo a further 

 chemical change, either in consequence of the partial disease 

 occasioned by the attack of the tubers, or in passing through the 

 substance of the tuber itself. We know that in the dark, plants 



3 H 2 invariably 



