PROGRESS OF MICROSCOPICAL SCIENCE. 
41 
and spore-cells. The former are either intercalated (“ enclosed ”) or 
terminal, usually cylindrical in shape and thin-walled without layers ; 
within is a parietal layer of protoplasm and a large central vacuole. 
Their breadth varies from 40-190 mm., and the length is generally 5-20 
times the breadth. On further examining the contents, it is seen that 
some of the cells have a layer of chlorophyll granules, the continuity 
of which is usually interrupted in certain parts, and sometimes to such 
a degree as to produce the appearance of a network ; other cells, how- 
ever, are almost deprived of chlorophyll, and have a much thinner 
parietal layer of protoplasm. In specimens which produce no spores, 
the green cells exist alone ; but in spore-bearing individuals both 
coloured and colourless cells are found, the latter being the “suh- 
sporal” cells spoken of above. The terminal cells are either like the 
ordinary coloured cells (only longer), or else they are twisted and 
usually branched above, forming what the author calls “ helicoid ” 
cells. These helicoid cells are common only in P. Cleveana, but they 
are of occasional occurrence on all the other species, with the ex- 
ception of P. Sumatrana and P. cequalis. As they are filled with 
chlorophyll, they must have an assimilating function ; but their form 
and a modification of their membrane evinced by its capacity to adhere 
to foreign substances, show that they are also organs of attachment. 
Reproduction takes place in two ways : by formation of spores, and, as 
the author quaintly expresses it, “by the bringing forth of prolific 
cells.” The cell (only occasionally a terminal one) destined to 
spore-production, first widens at its upper part, then the protoplasm 
in this part is increased by apposition from within at the cost of the 
protoplasm in the lower portion, and this transference is participated 
in by the chlorophyll, which penetrates into the widened portion and 
fills up the great central vacuole in it. After all (or rather nearly 
all) the chlorophyll has become collected in the upper part of the 
cell, it is shut off from the colourless, almost empty subsporal cell by 
the formation of a transverse partition. Finally, the spore is prepared 
for its season of rest by the thickening of its wall, and the transforma- 
tion of a part or all of its starch-grains (formed in the chlorophyll) 
into a brownish oil. Several deviations from this normal method are 
described : thus, the upper part of a cell destined to become a spore 
may not enlarge ; or a considerable part of the chlorophyll may 
remain in the subsporal cell, which, under these circumstances, either 
branches or else produces twin (sometimes triple) spores ; again, the 
spore may be formed in the lower part of the mother-cell. Moreover, 
sometimes in specimens of P. Cleveana where no rhizoid part is de- 
veloped, a spore may occupy the same place as the mother-spore, and 
possess the same membrane as its parent except at its upper part. 
The “ prolific ” cells are borne in most cases by sterile individuals ; 
they are nothing more than ordinary cells packed with starch -grains, 
and being only provided with a thin membrane, are not adapted to 
undergoing a period of rest. They become disunited from the decayed 
elements in connection with which they were formed, but their isola- 
tion is not so complete as to prevent two prolific cells remaining 
united and germinating in company, which latter process consists in 
