SIGILLARIEAE. 



253 



drawings, especially not in those that are less highly magnified. His 

 sections may have too regularly avoided this zone. For this reason I 

 give here a sketch of the central portion of a stem which was determined 

 by Renault himself and given by him to Williamson, who most kindly lent it 

 to me for the purpose of this drawing. I remark at the same time that the 

 specimens preserved in the Paris Museum are perhaps less irregular, but 

 have essentially the same character, and of this I have satisfied myself by 

 repeated examination. This is so far important as tending to make us less 

 inclined to the assumption of a pith surrounded by distinct bundles than 

 to the view that the whole 

 together is a central bundle- 

 strand, the centre of which is 

 parenchymatous, while portions 

 of the periphery are tracheal in 

 character to an extent not 

 exactly defined. And since, as 

 we know, the smallest narrow- 

 est elements lie on the outside, 

 the result would be a picture 

 similar to that which would be 

 produced for example in Le- 

 pidodendron Harcourtii, if its 

 tracheal ring were broken up 

 into separate portions, as is 

 actually the case in L. Jutieri. 

 And if this is the natural con- 

 ception as regards one species of 

 the genus, we are further driven 

 to adopt the same explanation 

 of the other species, Sigillaria 

 Menardi, which differs only by 

 its greater regularity and more 

 perfect consolidation. We can- 

 not enter further here into 

 the consequences which result from this view ; we should quickly arrive 

 by this path at the general conception already adopted by some authors, 

 namely that pith and peripheral ring of vascular bundles have been 

 formed by differentiation from the originally simple central strand. 

 Van Tieghem's 1 view is determined by the opposite idea, for he would 

 everywhere explain the axile cauline bundles as due to the coalescence 

 of several trace-bundles with their wood-portions turned one towards 



FIG. 29. Sigillaria spinulosa, Germ. Centre of the stem in 

 transverse section, showing the ring of primary wood divided into 

 irregular bufjdles, and the inner portion of the secondary growth. 

 Drawn from a specimen in Williamson's collection presented by 

 Renault himself. Slightly magnified. 



van Tieghem (2). 



