Some years elapsed before Hales' labours added materially
to the progress which had been already made in the study of
these processes in vegetation. His important services to
vegetable physiology close our present period, but before we
pass on to them, we must first notice a few less important
writers. The pages of Woodward and Beale on transpiration
and the absorption of water are not very valuable contributions
to the theory of nutrition. The fact stated by Woodward,
that a Mentha growing in water took up and discharged by
evaporation through the leaves forty-six times as much water
as it retained in itself, was perhaps the most important of all
that he discovered, but his own conclusions from it were of no value.
None of Malpighi's doctrines had from the first excited so much attention as the one which makes the air which is necessary for the respiration of the plant circulate in the spiral vessels of the wood, as it does in the tracheae in insects; while Grew and Ray after him agreed with Malpighi in the main, his countryman Sbaraglia in 1704 ventured even to deny the existence of such vessels, and before long phytotomy was fallen into such a state of decadence that the question, whether there were any vessels, or as they were then called spiral vessels, at all, was repeatedly affirmed and as often denied again, and ultimately it was thought better in the interest of physiological questions to take counsel of experiment rather than of the microscope. Thus in 1715 Nieuwentyt endeavoured with the help of the air-pump to make the air contained in the vessels issue in a visible form under a fluid. Here we again encounter the philosopher Christian Wolff as a zealous representative of vegetable physiology in Germany ; in the third part of his work, 'Allerhand niitzliche Versuche,' 1721, among other experiments he mentions some which confirmed the presence of air in plants; the question was more interesting, in the state in which physics and chemistry then were, than that of the anatomical character of the air-conducting organs.
