in Rhodymeniales : II. Delesseriaceae. 177 
mature the fructification assumes a dark-red colour, from the 
dense ‘ nucleus ’ of highly-coloured carpospores. 
It would appear, therefore, that the so-called stalked cysto- 
carp is more accurately described as a minute flattened 
branch, upon one of the surfaces of which an urn-shaped 
cystocarp has arisen. 
It is, however, with the minute structure of this cystocarp, 
and the details of its process of maturation, that I am chiefly 
concerned. In order to make the following description in- 
telligible, it is necessary to recall the histological structure of 
the sterile fronds of Delesseria sanguinea and its congeners. 
This has been the subject of detailed investigations by several 
observers, and it appears that these species conform rigidly to 
the law of growth of the Floridean thallus first clearly 
enunciated by Schmitz (’83). That is to say, the growth is 
exclusively apical, no transverse division ever occurring in 
a segment cut off from the apical cell, and no longitudinal 
division passing through the organic axis of the segment. It 
is true that Schmitz, returning to this subject later (’92), 
somewhat limited the application of this law, excluding in 
particular from its operation the tribe Nitophylleae of the 
order Delesseriaceae. The tribe Delesserieae, which, standing 
as it does next to the excluded tribe, it may be assumed that 
Schmitz examined afresh, was, with the large majority of 
Florideae, still regarded as falling under the law of exclusive 
apical growth. With this view I agree, as I have seen 
nothing in my observations on Delesseriaceae which could be 
regarded as evidence of intercalary cell-division. Wille (’87) 
has, it is true, both described and figured intercalary cell- 
formation as occurring in D. sanguinea in the axial row of 
cells during the course of the development of the midrib. 
As, however, he makes the statement incidentally and without 
comment, although Schmitz’s work had been published some 
years before, it is probable that the statement was based on 
a too superficial observation of the thallus. The cells shaded 
in Figs. 1 and 3 of Taf. I of his work, are the products 
of the pericentral cell lying immediately above the central 
