Among the distinctive characters of this species, used by Rosanorr, in his 
important paper on the Melobesiacez, the want of “heterocysts” has been of special 
importance in distinguishing it from M. farinosa, as it permitted determination even 
in cases where the characters taken from the organs of reproduction could not be 
used. As shown by FosLıE however, |. c. p. 103, the cells situated under the dicho- 
tomies are often larger than the others and resemble the heterocysts of M. farinosa. 
I can confirm Foslies statement, having frequently found these cells in Danish 
specimens of M. Le- 
jolisii. They agree 
indeed completely 
with the hetero- 
cysts of M. farinosa, 
in bearing a hair 
or a scar left by 
a shed hair, in 
being poorer in 
contents and in 
bearing no cortical 
cellsas do the other 
cells of the mono- 
stromatic frond. 
But they differ 
from the hetero- 
cysts of the last- 
named species in 
being derived, not 
18, 
from end-cells of Fig. 156. 
filaments, which Melobesia Lejolisi, from Birkholm, Sf. A, vertical section of marginal part of frond, 
* trichocyte. B, monostromatic frond seen from above; below a trichocyte, numerous 
fusions. C, marginal part of frond seen from above; two trichocytes are visible, one 
further, but from with hair. D, vertical section, not median, through a sporangial conceptacle; only un- 
divided sporangia present. E, vertical section through emptied sporangial conceptacle. 350: 1. 
do not develop 
cells situated under 
a ramification. I have convinced myself that this difference really exists by exami- 
ning authentic specimens of M. farinosa. Where the included heterocysts of this 
species are present it is easily seen that the two cell-rows, the separating line of 
which goes in continuation of the heterocyst, are not given off from this, but from 
the adjacent cell-rows. As shown by Sous (Cor. p. 24), these cells produce a hair 
without formation of a transverse wall. The hairs are, according to the mentioned 
author, very short-lived, and fall off after a separation has taken place at their base 
by local incrassation of the longitudinal wall. This is also the case with those of 
M. Lejolisii; sometimes, however, they are more persistent, and appear as long 
hyaline hairs (fig. 156 C). Their wall is stained very intensely by hæmatoxyline, 
by which they become very obvious, and the same is the case with the basal part 
