CHAP, in.] of Cell-membrane in Plants. 279 



celled parenchyma that surrounds them. Thus the peculiar 

 character, the idea, of the vascular bundle was brought promi- 

 nently into contrast with that of other forms of tissue. This 

 took the place of the distinction between rind, wood, and pith, 

 which had served former phytotomists as the basis of their 

 histological survey, but which is in itself only a secondary 

 result of the later elaboration of certain parts of the plant. 

 Moldenhawer, in laying the chief stress from the first on the 

 contrast between vascular bundles and parenchyma, hit upon 

 a histological fact of more fundamental importance, the right 

 appreciation of which has since enabled the phytotomist to 

 find his way through the histology of the higher plants. For 

 while the construction of Monocotyledons and Ferns must 

 seem abnormal and quite peculiar to any one who starts with 

 examining the rind, wood, and pith of old dicotyledonous 

 stems, those on the contrary who, with Moldenhawer, have 

 recognised a special histological system in the vascular bundles 

 of Monocotyledons, have the way opened to them to seek for 

 a similar one in the Dicotyledons, and to refer the secondary 

 phenomenon of wood and rind to the primary existence of 

 vascular bundles. Moldenhawer did in fact open this way, 

 when he showed how the growth of a dicotyledonous stem 

 may be understood from the structure and position of the 

 originally isolated vascular bundles (' Beitrage,' p. 49, etc.). But 

 he was thus of necessity led to the rejection of Malpighi's 

 theory of the growth in thickness of woody stems, which all 

 vegetable anatomists from Grew to Mirbel had adopted. 

 Though Bernhardi and Treviranus made weak attempts to 

 discredit it, Moldenhawer was the first who distinctly rejected 

 the origin of the external layers of wood from the inner bast, 

 and proposed the first really practical basis for the later and 

 correct theory of secondary growth in thickness (p. 35). The 

 removal of this ancient error is in itself a very important 

 result, and one which, apart from all other services, must 

 secure him an honourable place in the history of botany. 



