40 ox GROWTH AND EXTENSION IN THE VEGETABLE KINGDOM, 



Malpiglii, the discoverer of spiral vessels,* considered tliem as 

 air-tubes on account of their analogy with the air-tubes of 

 insects, which he also discovered and named trachece, a name 

 ahnost universally adopted. As early as the commencement of 

 the eighteenth century (1709), Magnol observed that coloured 

 fluids ascended in cut branches even up to the flowers, an obser- 

 vation repeated by many others, but Reicliel in Leipzig first saw 

 (1758) that tliey only ascended in tiie spiral vessels. Thence 

 Hedwig was of opinion (1790) that these vessels might be at once 

 air and sap vessels, only that the sap rose merely in the hollow 

 spiral thread. It is, however, not hollow. The thing became 

 doubtful again when it was ascertained that coloured fluids did 

 not ascend in plants which had put forth uninjured roots in the 

 earth or in water. It was therefore thought, not without reason, 

 that coloured fluids only ascended in spiral vessels by capillary 

 attraction, consequently only in the open vessels of cut branches.^ 



In the bark which consists of parenchyma only, without 

 vessels, the sap does not rise from the earth. Stems and branches 

 of trees can be deprived of their bark all round (ringed), and 

 they only bear the more flowers and fruit, as is well known to 

 gardeners. The sap therefore does not rise directly through the 

 walls of the cells, as many believe, also not through tiie intervals 

 between the cells — the intercellular passages, as first Treviranus 

 and afterwards De Caudolle believed. We see not why, if the 

 sap penetrates so easily through the cells of the parenchyma, it 

 should not rise rather through the bark, of which the texture is 

 so much looser than that of the wood. In spring, when the 

 stems of birches are tapped, the bark remains quite dry, whilst 

 the sap flows copiously from the lacerated wood-vessels. 



But in most plants the wood does not consist entirely of vessels, 

 but also of cellular tissue, and it is still a question whether the 

 sap rises through the vessels or through the cellular tissue. In 

 the first place it must be observed, that through whichever it 

 may rise, it can pass sideways through the vascular or cellular 

 tissue as readily as it rises upwards. To prove this we have only 

 to cut a branch through to the pith in a spiral line, so that no 

 sing-le vessel or row of cells remains unbroken from the base to 



* Malpighi first described and figured these vessels. That Grew saw 

 them as soou as he made use of strong magnifying powers was to be expected, 

 but he only described them at a later period than Malpighi. 



t Schleiden, indeed, says (System. I3ot., vol. i. p. 232), " Do they know 

 what capillary attraction is ? Strong walls are necessary for it, not thin 

 membranes iu a turgescent tissue." But Schleiden does not think of blot- 

 ting-paper, in which it is well known that water rises by capillaiy attraction 

 without strong walls. When it is full of water, it is quite true that nothing 

 more will rise into it. 



