298 Scott and Brebner. — On Internal Phloem 
M. Lamounette’s careful observations on the origin of the internal phloem in the 
growing point of the stem are of great interest. He finds that it always arises later 
than the normal tissues of the bundle, and that it is of medullary, not of procambial 
origin. The distinction in some cases is certainly a very fine one, and we have not 
always been able to detect it, but we willingly accept M. Lamounette’s results. We 
hope that our further investigations may throw additional light on this author’s 
interesting hypothesis that the phylogenetic origin of all internal phloem is to be 
traced to independent medullary strands, unconnected with the normal bundle- 
system. 
Two other papers have lately appeared, bearing on our subject. Leonhard’s 
Beitrage zurAnatomie der Apocyneen (Bot. Centralblatt, Bd. XLV, 1891) confirms 
the general occurrence of internal phloem throughout this order (with one doubtful 
exception). The author appears to have found phloem embedded in the wood in 
Lyonsia , though his description is not perfectly clear, as he does not distinguish 
between interxylary and intraxylary phloem. 
Quite recently M. Herail has published a preliminary note on medullary phloem 
in the root (Comptes Rendus, April 13, 1891). He has discovered this structure 
in the adventitious roots of Vinca major and V. media , but not of V minor , in 
which the pith soon becomes sclerotic. He points out the necessary condition on 
which the occurrence of medullary phloem in the root manifestly depends ; namely 
the presence of a permanently parenchymatous pith. He cites Van Tieghem’s 
observation of internal phloem in the root of Cucurbita , but is not acquainted with 
our description of this tissue in the root of Strychnos, published in 1889. M. Herail’s 
observations are a welcome addition to our own. 
D. H. S. & G. B. 
