66 ON THE OCCURRENCE OF GALLS IN RHODYMENIA PALMATA. 
own earlier investigation of such bodies at Penzance) that they 
were possibly of the nature of galls, I was yet ee without a clue to 
their origin, or even a conjecture as to their development. The 
surface of the Boctat ponte of the frond is covered with minute 
papille, and s these papilla appear to be composed 
of at rm dae 5 esta to the thallus. The normal cortical 
cells of the Rhodymenia frond are continuous with those of the 
) outgro 
of the gall gece thicker walls than the corresponding layer of 
the thallus. The central cells of the papilla, however, have often 
thick or dinelotied: conten . ey matter remained at this stage 
until Mr. Murray collected several specimens, which he brought to 
me, showing a further aivslapmnene of the galls. These were in 
fact a series of intermediate stages between those p 
apille and 
definite proliferous outgrowths sprouting from the flat surface of 
the frond, and exactly resembling in shape ond structure the well- 
known marginal roliferations characteristic of Rhodymenia pal- 
mata, though never attaining the same dimensions. These ~~. 
ics 
in their ctipeseegie ape ood. However: this is merely conjecture, sin 
the holes and pits may = accounted for by the ravages of the 
animal I am abo = to des 
The matter r peaSined in “this position ao I was able 
resume its fiiveetightion in the British Museum on the certs 
material. It was then found that in the eirioel of the papille 
there were numerous lesions the tissue of the thallus; whole 
process (fig. 6). In these diseased portions, and in the neigh- 
bouring cells and intercellular spaces, there were found plentifully 
roun es of animal nature, which in some cases look like eggs 
and in others like digested cells of Rhodymenia. These tracks, as 
has been said, are always i in the region of the papille, though the 
latter are occasionally found at some little distance (never far) from 
them, showing that the irritation is propagated over the adjoining 
area. Closely sre ei with the galls and with the more de- 
o ou and occasionally occurring among their basal 
cells as well as bnew ere in the affected region, are to be found 
yellow masses, sometimes filling a cell or several adjacent cells or 
intercellular spaces. The nature of this yellow substance I have 
been unable to ascertain, but if may be mentioned that it resists 
the prolonged action of so powerful a solvent as ether; it also 
resists acids, at least in a higher degree than the ¢ cell walls, but it 
one slightly to exposure overnight > ammonia. Whether this 
substance be a direct secretion of the animal in question, or a ge 
product of the diseased plant tissues, ri] cannot say; but from i 
OP ae en of course, occur sometimes normally on the flat surface of the 
