in the Root and Stem of Dicotyledons. 297 
We are indebted for our material partly to the Director of 
the Royal Gardens, Kew, partly to Mr. H. N. Ridley, of the 
Botanic Gardens, Singapore, who has been so kind as to send 
us a number of specimens carefully preserved in spirit. 
We have further to thank the officers of the botanical 
department of the British Museum, and also Mr. B. Daydon 
Jackson, Sec. L. S., for their kind help in the nomenclature of 
species. 
POSTSCRIPT. 
When this paper was completed in December, 1890, we had not seen the work 
of M. Lamounette, f Recherches sur Forigine morphologique du liber interne/ 
which appeared in November, in the Annales des Sci. Nat., Bot. Ser. 7. T. XI. 
M. Lamounette has made a number of valuable observations on the origin of 
internal phloem in the hypocotyl, the cotyledons, the terminal bud of the stem, 
and the leaves. He strongly supports the views of M. Herail, and rejects the term 
‘ bicollaterality ’ in all cases, even in the Cucurbitaceae (p. 264). He regards the 
internal phloem as being due to an ulterior evolution of the medullary cells, ana- 
logous to the formation of periderm in the cortex (p. 235), and considers that it 
was primarily independent of the normal bundles, its close association with them 
in the Cucurbitaceae not having been attained at a later phylogenetic stage. His 
view of the internal phloem as an 1 acquired character ’ which has become heredi- 
tary (p. 278) is evidently beyond criticism in the present state of our knowledge. 
As regards the transition from stem to root, M. Lamounette says that the internal 
phloem, when present in the hypocotyl, is altogether formed in the medullary 
parenchyma, and not in any degree at the expense of the phloem of the root 
(p. 277). He appears to attribute the opposite view to Gerard. Surely there is 
some confusion between course and development here. In the cases investigated by 
Gerard and by ourselves there is no doubt as to the continuity between the internal 
phloem of the hypocotyl and the external phloem of the root, but no one has ever 
supposed that the one is developed from the other. M. Lamounette appears to 
have overlooked this continuity in all cases, a fact which is probably explained by 
his having worked chiefly with very young seedlings. He rightly points out that 
the development of the internal phloem in the hypocotyl often takes place very late 
as is especially the case in Ipomoea (p. 243). In the Onagraceae he finds that in- 
ternal phloem is entirely absent from the hypocotyl, the cotyledons, and even the 
earlier-formed leaves (pp. 245 and 274). So far as the hypocotyl is concerned this 
can only be true of very young plants, for we know from Weiss’s observations above 
cited that the internal phloem is here continued into the root, when it forms the 
innermost interxylary phloem-strands (see above, p. 272). We suspect that in all 
cases continuity between the internal phloem of the stem and the phloem of the 
root exists, though the connection may no doubt be established relatively late in 
some cases. 
