42 ON GROWTH AND EXTEiNSJON IN THE VEGETABLE KINGDOM. 



the colouring matter not in all the cells ? His fig. 9 shows that 

 the latter is the meaning intended. Now how does the colouring 

 matter get into the upper cells if it must go tlirough the lower 

 ones ? That is to me quite unintelligible. But I can readily 

 understand that the juice rises through the vessels — the spiral 

 vessels — to the top, and then rapidly passes into the adjoining 

 cells here and there, according to the nature of those cells. We 

 have seen how readily the sap spreads laterally even in hard 

 woody tissue, and it must be expected to do so much more 

 readily in the softer parts. 



It is not credible that the sap should rise in the piosenchyma- 

 tous cells, for example, in the birch, and not through the spiral 

 vessels. I have, in my Lectures on Natural History, Plate 2, 

 Fig. 1, figured a longitudinal section of birch wood at tlie time 

 when it gives out the sap. With age the vessels enlarge, and 

 probably become inactive, and they only appear to become 

 divided by cross partitions, by growing together by their ends. 

 Coloured liquids penetrate through these cross partitions, as I 

 have shown, Plate 5, Figs. 4 and 5 of the Anatomy of Plants. 

 I may add that Conifers are as little injured as other trees by 

 ringing, or taking otf the bark in a ring round the stem. Now 

 there is no cellular tissue in the wood of these trees, but it con- 

 sists entirely of vessels, and the sap cannot rise otherwise than 

 through the latter. 



From all this I draw the conclusion that spiral and porous 

 vessels carry the sap over the whole plant, but soon discharge it 

 into the surrounding parts, so that they generally appear empty, 

 and look like air-vessels. 



No operation shows more the true mode of action in plants 

 than grafting (including budding*). The plant is a compound 

 organised body, of which every bud can live and be developed 

 independently. The bud may be planted in the earth by cut- 

 tings, or on another plant by grafting or budding. In the latter 

 case the graft converts the sap of the stock into its own sap in 

 the same manner as the cutting converts the juices of the earth 

 into its sap. The stock has no other influence on the graft but 

 that which the soil has on a plant ; the latter will not grow in a 

 soil which does not suit it, and the graft will only grow upon 

 plants allied to it ; the plant succeeds better in one soil than in 

 another, so the graft succeeds better on one stock than on 

 another ; the plant is developed earlier or later, according to 

 whether the soil is moister and warmer or drier and colder ; the 

 earlier or later shooting of the graft is in some measure regulated 



* Veredeln of German gardeners, literally ennobling, includes both graft- 

 ing and budding. 



