CHAP, in.] of Cell-membrane in Plants. 263 



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 enter- 

 tained 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. BERNHARDI'S short treatise, ' Beo- 

 bachtungen liber Pflanzengefasse,' 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. 



1 Johann Jakob Bernhardi, born in 1774, was Professor of Botany in 

 Erfurt, and died there in 1850. 



