288 EEV. PROF. G. HENSLOW ON THE [Aug. I907, 



indicating a watery environment ; but a study of his photographic 

 illustrations really indicates the opposite conditions. The purport 

 of the paper is to describe and figure a vascular connexion between 

 the protoxylem ^and the outer cortex. A sort of cellular ' arm ' 

 containing tracheids extends from the stele to the outer cortex, to 

 allow of water being absorbed at one place on the circumference and 

 conveyed to the central vascular bundle ; the rest of the inner cortex 

 is composed of compact, very delicate cellular tissue, the cells of the 

 ' arm ' having seemingly rather thicker walls. In referring to his 

 figs. 1 & 2, pi. xxvi, the author observes that 



* the middle cortex appears in these to be entirely absent, as is the case, indeed, 



in the majority of Stigmarian rootlets A small process ( p) passing off from 



the parenchymatous sheath [of the stele] would seem to have connected it with 

 other parenchymatous cells of a delicate character, forming lacunar [?] or 

 trabecular [?] tissue, remnants of which can be seen near the upper end of this 

 strand, as also in Renault's figure.' {Op. cit. pp. 560, 561.) 



A very careful and searching examination of these figures with a 

 lens reveals nothing like ordinary trabecule, as the reader will see 

 by comparing Dr. Weiss's figures with one given by Dr. Scott of a 

 root of Calamites (' Studies in Fossil Botany ' 1900, fig. 14, p. 39). 

 Something more definite of this nature would undoubtedly have 

 been seen in some of the sections of Stigmarian rootlets. 



Examining Dr. Weiss's fig. 3, a delicate cellular tissue seems 

 pretty clear. Numerous more or less hexagonal spaces are marked 

 out ; and thus what Dr. Weiss would call lacunae, I would suggest to 

 have been delicate water-storage tissue, which has almost 

 completely disappeared from fig. 3, and in many cases has gone alto- 

 gether. Fig. 4 might give a false impression of a single trabecula 

 connecting the cellular sheath of the stele with the outer cortex ; 

 but this would be contrary to all experience with aquatic roots and 

 stems. A reference to fig. 3 shows that the surrounding, inner 

 cortex was present. Figs. 4 & 5 show a zone of thick-walled cells, 

 only ' broken ' where the stelar arm runs into the outer cortex. This 

 carries the tracheids to it on the inside, as in fig. 5, or through it, 

 as in fig. 4. Larger thin- walled hypodermic cells on the outside 

 show where water is absorbed, while the tracheae convey it to the 

 interior. Had these rootlets been in a saturated medium, there 

 would have been no necessity for these cellular processes at all. 

 This method is well known in certain xerophytes, in their leaves. 

 Thus Reaumuria and its ally Tamarix secrete salts during the 

 period of root-absorption. But, in the hot season, they absorb dew, 

 and convey it internally by means of large distorted tracheids. 



It may be added here that Dr. Weiss's figures show no lacunae of 

 the ordinary type seen in aquatic plants, nor aerenchyma of swamp- 

 trees of the tropics, nor pneumatophores of marine mangroves, nor 

 anything like those of the swamp-cypress of Florida. 



Fig. 5 has what Dr. Weiss calls ' trabeculae ', consisting of one or 

 two very minute cells, which appear to separate larger, thick -walled 

 spaces of the same size as the single cells of the inner cortex ; but 

 whether they were air-chambers or not is scarcely apparent. At all 



