ON GEONYIH AND EXTENSION IN THE VEGETABLE KINGDOM, o3 



granules, sometimes without a nucleus, but also frequently with 

 an evident larger or smaller nucleus inclosed in a membrane, 

 lying in different positions in relation to the cell, as is the case 

 in fully-formed cells. Sometimes we find in these young cells, 

 as in fully-formed ones, two nuclei in one cell. If tlie cambium 

 is allowed to dry, it changes entirely into a mass of roundish, 

 irregularly shaped granules, adhering in strings, amongst which 

 are a few larger globules. In the cambium of this willow branch 

 were a few green cellular nuclei ; as it dried, the whole mass 

 became green. It is therefore clear that the granules and cells 

 were generated in a mucilaginous mass ; that round the granules 

 a membrane is first formed which is the skin of the nucleus; 

 and round this another forming the proper cellular walls ; and 

 that all these granules and membranes were in a mucilaginous 

 state. 



There can be no doubt that the mucilaginous generative sap 

 proceeded from the adjoining cells, and exsuded through their 

 walls. In the case of the willow roots this was evident, and the 

 cambium lying between tlie wood and the bark can only have 

 been produced in tliis manner, either from the wood or from the 

 bark, or from both at once. No mouths of any vessels can be 

 anywhere found from which this sap can have issued. That in 

 the animal kingdom nutrition takes place by exsudation from the 

 finer vessels is now generally acknowledged ; but this exsudation 

 is known to be a penetration through invisible fissures or pores.* 

 And the growth of many parts in plants cannot be otherwise ex- 

 plained than by supposing them to enlarge, and that a fluid 

 issues from them, from which are generated specific bodies. 

 Thus the young wood is formed between the old wood and the 

 bark ; thus the bast bundles in the bark are enlarged and 

 separated from the other portions ; tlius also do the single vessels 

 grow in monocotyledons. A distending power must necessarily 

 be ascribed to plants, in order to make room for the new por- 

 tions, and for the sap which exsudes for their formation ; strong 



* Schleiden is indeed of opinion (Systeraat. Bot., vol. i. p. 286), that the 

 assuming the existence of invisible pores is a superfluous and unsupported 

 hypothesis ; that the relation between a membrane and water is the same as 

 that between salt and water, only that the membrane does not become fluid, 

 because it only absorbs a small quantity of water. When we carefully pour 

 pure water over a solution of gum and sugar, the two liquids first remain 

 unmixed, then the dense liquid absorbs the more diluted oue, and this lasts 

 until the two are mixed together almost uniformly. But molecules of 

 sugar are not molecules of water, and the former must have taken their 

 places amongst the latter: these places are interstices — are invisible pores, 

 not empty spaces, it is true, but variously occupied. If we put powdered 

 sugar into Seltzer water, we see the molecules of sugar expelling the mole- 

 cules of carbonic acid, in order to take their place. 



VOL, VI. D 



