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AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
he found sieve tubes and companion cells crushed, but never phloem paren- 
chyma. 
Publications on the changes undergone by the phloem of herbaceous 
types are few. Schumann (1890), in his work on the anatomy of the com- 
posite stem, reports finding lignification of the sieve tubes and companion 
cells in two species of Compositse, Scorzonera Hispanica and Aster thyrsi- 
floruSj finding the sieve plates especially to be lignified. Boodle (1902), in 
his first note on the subject, reports finding lignification of the sieve tubes 
and companion cells in two plants of Helianthus annuus; lignification of 
contents, though not of the walls of sieve tubes, was obtained in the root. 
In repeating the work of Vesque and Boubier, Boodle found no lignification 
of sieve tubes in Betula alba, such as had been described by these workers. 
In a later publication. Boodle (1906) reported results of the examination 
of additional material of Helianthus, in the course of w^hich examination he 
investigated eleven plants of H. annuus, one plant of H. tuberosus L., and 
the stems of H. laetiflorus Pers. and H. decapetalus L. The observations 
previously recorded were confirmed both for H. annuus and for the other 
species mentioned. His conclusions may be summed up as follows: the 
sieve tubes and companion cells in the stems of the species mentioned are 
normally lignified; the contents of the sieve tubes in the root become ligni- 
fied, whereas lignification of phloem parenchyma is rare, having been ob- 
served in only one case. 
The present investigation was undertaken to determine whether there 
exist any departures from the usual unlignified and uncrushed condition 
of the phloem in herbaceous types, without reference to certain alterations 
known to be brought about by diseased conditions, such as phloem necrosis 
in leafroll of potatoes. 
In order to determine the occurrence of such unusual conditions, the 
mature stems of a large number of herbaceous plants were examined by 
means of free-hand sections.^ No conditions departing from the usual were 
found, until species of the Compositae were examined. In a number of 
species of this family extensive lignification of the phloem was found to 
have taken place. This lignification would seem to include only the 
parenchyma of the phloem, other elements presenting the usual appearance 
of a phloem group of the herbaceous type. The lignified elements appear 
with greatly thickened walls, and, but for their position, would in most 
cases be difficult to distinguish from the tracheids of the xylem. In a 
phloem group in which such lignification is found, it is practically certain 
that all of the phloem parench3/ma becomes lignified, with the exception 
of those elements most recently formed, found next to the cambium. The 
parenchyma cells of this region, upon reaching maturity, will of course 
^ The sections were stained on the slide with phloroglucin and concentrated hydro- 
chloric acid, the lignified portions giving the characteristic reaction. Portions of stems 
showing typical lignification were then imbedded in celloidin, sectioned, and stained with 
haematoxylin and safranin. 
