STRUCTURE AND DEVELOPMENT OF SORANTHERA. 485 
belonging to Hlachistacee, Chordariacee, and Ectocarpacee. Many 
of these have been described by M. Sauvageau, * Sur quelques 
Algues phéosporées parasites" (Journ. de Bot. tom. vi. 1892). 
In Soranthera the cells at the base of the plant in all but the 
very youngest stage elongate to form septate rhizoids, which 
intertwine and encircle the thallus of the host, Rhodomela Larix 
(Pl. 24. fig. 13). The walls of these rhizoids are very thin and 
stain deeply, but of their contents it is not possible to speak 
without living material. On reaching the host they become very 
closely adpressed to it, and after growing round it for a short 
distance, the ends penetrate into the thallus. Here they push 
their way through the cells, disorganizing the host tissue and 
developing small knots of minute cells, which are presumably 
haustoria (Pl. 24. fig. 14). It is true that there are certain 
groups of cells growing from the rhizoids still outside the host 
plant which strongly resemble the supposed haustoria inside the 
Rhodomela thallus. But this does not necessarily prohibit the 
possibility of these latter being of the nature of haustoria. 
It is probable that the investigation of other plants, hitherto 
supposed to be merely epiphytic on some one special alga, may 
lead to the enlargement of the number of parasites among the 
Pheophycec. 
In conclusion, I wish to express my thanks to Mr. Blackman 
for kindly helping me in the manipulation of the microtome, 
while cutting the necessary series of sections; and I gratefully 
acknowledge the debt I owe to Mr. Murray for placing this and 
other valuable material in my hands. 
EXPLANATION OF THE PLATES. 
Prate 23. 
Fig. 1. Soranthera ulvoidea. Nat. size. 
2. Young plants on Rhodomela Larix. X 8. 
3. Transverse section of young thallus. X 65. 
4. Central cells of slightly older plant. X 65. BEEN 
5. Peripheral layer of still older plant, showing remains of assimilative 
filaments. x 375. 
. Possible plurilocular sporangia. X 319. 
. Young eryptostoma. X 979. 
. Cells round older eryptostoma, di 
and unilocular sporangia. X 979. 
9. Mature sorus of unilocular sporangia. 
ON C: 
viding to form sorus of paraphyses 
x 140. 
