Chap, hi.] of Cell- membrane in Plants. 283 



which he understood better. All these ' vasa propria ' he took 

 for cellular vessels, formed of tubes opening into one another ; 

 but he clearly distinguished the turpentine-ducts from them, 

 and has given a correct figure of such a duct from the pine, 

 though he assumes the existence of a special membrane lying 

 inside the cell-rows which surround it, and lining the passage. 

 Finally he passes on to the intercellular spaces, which he con- 

 siders to be gaps in the cellular substance, and illustrates by 

 Musa and Nymphaea. He does not notice particularly the 

 narrow interstices which Treviranus had observed traversing 

 the parenchyma. 



In the second portion of his work he includes all the vessels 

 found in the vascular bundle of the maize-plant under the 

 term spiral vessels, but he distinguishes the different forms of 

 them well, and especially points out that rings and spirals 

 appear on one and the same vascular tube in different parts of 

 its course, as Bernhardi had already shown. The isolating of 

 the vessels gave him a better opportunity of seeing how they 

 are made up of portions of different lengths than his prede- 

 cessors had enjoyed, and he proves at some length the existence 

 of a thin closed membrane forming the vessel, but like Hedwig 

 he places the thickenings on the outside. He as little overcame 

 the difficulties of bordered pits as did von Mohl and Schlei- 

 den after him. In this case as in others, it was the history of 

 development which first taught the true nature of these form- 

 ations (Schacht, i860). 



It was mentioned in the Introduction that Moldenhawer 

 may be said to close the first portion of the period from 1800 

 to 1840, not only because the majority of the questions ven- 

 tilated up to that time were to a certain extent settled by him, 

 but also because there is no material advance in phytotomy to 

 be recorded for several years after the publication of his work 

 in 1812. It is true that Kieser in his * Grundziige der Ana- 

 tomie der Pflanzen' (1815) attempted a connected exposition of 

 the whole subject, but his book offers nothing really new, 



