Page:History of botany (Sachs; Garnsey).djvu/283

 and Grew he supposed that the spiral vessels had no wall of their own, but thought that the closely-rolled spiral threads formed a wall; the constrictions in broad short-membered vessels he regarded as real contractions in their substance, caused by the increased tightening of the spiral threads through a sort of peristaltic movement, a mistaken notion often entertained at the beginning of the century, by Goethe among others, and connected with ideas of vital power prevalent at the time. In the stomata, to which he gave the name still in use, Sprengel like Grew, Gleichen, and Hedwig, saw a circular cushion instead of the two guard-cells; but he notices the observation first made by Comparetti, that the orifice closes and opens alternately, being wide open in the morning and closed in the evening. But he considered the stomata to be organs of absorption.

Sprengel in enunciating his own theory of cell-formation accused Mirbel of mistaking the starch-grains in the cells for the pores of the cell-walls. On this point, so important in the doctrine of the cell and in physiology, he was followed by the three candidates for the Gottingen prize, though Bernhardi had in 1805 defended Mirbel's view, and had pointed out how little likely it was, that so skilful an observer as Mirbel should fall into so gross an error. short treatise, 'Beobachtungen über Pflanzengefässe,' Erfurt (1805 '), was in general distinguished by a variety of new and correct observations, and was the work of a simple and straightforward understanding, which takes things as they are presented to the eye without allowing itself to be led astray by preconceived opinions. His observations are certainly the best in the whole period from Malpighi and Grew to the younger Moldenhawer; his method of dealing with questions of phytotomy is much more to the purpose than that of the three rivals for the Gottingen prize.