112 MR. H. M. WARD ON THE STRUCTURE, DEVELOPMENT, 
Coleochete, forms occur where the cell-rows are not laterally united, but branched loosely 
as in the typical species of Chroolepus. 
But the importance of these analogies comes out more strongly if we compare the 
organization of the “fertile hairs "—each of which, be it remembered, is a production 
of the end cell of a series of thallus-cells—with what Gobi found in Chroolepus 
uncinatus*. 
This species occurred, mixed with C. wmbrinus, on the bark of trees around St. Peters- 
burg, in the spring and summer of 1871, as minute aggregations of loose or compacted cell- 
masses. The vegetative cells were made to pass through just such changes of colour as I 
have described, and as Cunningham noticed, according to the state of moisture or dryness 
of the atmosphere ; by keeping one half of a specimen wet in sunlight, it turned green, 
the dry half remaining orange-red. In the cells of the latter were red oily drops, which 
in the moist specimens decrease in quantity, and form mere red spots in a green matrix, 
or disappear. The reverse effects were obtained on altering the conditions ; and similar 
phenomena were observed on rocks, bark, &c. in the open. 
The cells which form zoospores are always orange-red ovoid dilatations situated on short 
curved pedicles developed from the sides or apices of the vegetative-cell series. If the 
figures on Gobi's plate are compared with Cunningham's fig. 2, or my figs. 21, 24, 31, 40с., 
it will be seen that what I have termed a “fertile hair" might almost be replaced by a 
fertile thread of Chroolepus uncinatus. The chief differences are the fewer numbers of 
zoosporangia in the tuft, the less evident central cell, and thinner walls of the Chroolepus. 
The oblique insertion of the pedicels at the lower third of the ovoid zoosporangium and 
their mode of attachment by a double ring, the papilla at the base of the latter resulting 
from a change in the cell-wall, the deep orange-red colour, size, and what details are 
given of the development, simply recall what I have described. 
Moreover these free sporangium-bearing threads pass down to cell-series which are 
spread flat on the substratum. _ Шуе supposed the irregular distribution of these “ vege- 
tative cells," to be replaced by a more orderly arrangement, due simply to simultaneous 
divisions in all the equivalent parts, a disk like that of Coleochete, or the above-described 
Alga would result; from this disk would spring the sporangium-bearing filaments as 
“ fertile hairs.” І believe it is not going too far to carry these analogies one step for- | 
ward, and imagine what would result if some of the zoosporangia never became raised 
above the surface, but remained in the thallus thus produced; if so, we could explain the 
zoosporangia of the thallus in the tropical Alga, and account for the extraordinary agree- 
ments in their position (as regards cell-series), size, &c., and formation of zoospores so 
like those from the “ fertile hairs " in size, form, colour and number, &c. If some such 
agreement does not exist, I see no escape from the temporary conclusion that a loss of 
function occurs here, or, if the zoospores prove capable of germination, that a case of 
apogamy is established. à 
I believe that the foregoing comparison is a sound one, and that the tropieal Alga 
(which still lacks a name) must be looked upon as a higher development of the Chroolepus 
ж * Algologische Studien über Chroolzpus,” in Bull. de l'Aead. Imp. des Sc. de St. Pétersbourg, tom. xvii. 1872, 
p.123. І have to thank my friend Mr. W. T. Thiselton Dyer for calling my attention to this important memoir. 
