320 Sykes. — Anatomy and Histology of Macrocystis pyr if era and 
of these the callus stained with Water blue or London blue, and in two 
only with London blue. In the sieve-tubes of the pith and in the cross 
walls of several of the hyphae numerous callus-rods were found, some of 
which stained only with London blue, while a few of the more central 
elements contained callus which gave the characteristic reaction with Water 
blue. Threads traversing the young sieve-plates, and slime-strings in the 
older sieve-plates, were satisfactorily demonstrated in a few cases, and 
several inner sieve-tubes, probably primary pith filaments, were found 
to be entirely filled with callus which stained with London blue and 
Russow’s callus reagent, and sometimes with Water blue. 
It is probable that, if well-preserved material were examined, Laminaria 
digitata would yield results similar to those obtained from L. saccharina. 
Alaria esculentea , Grev. Some material pickled in Formalin was 
examined by the Safranin method. The results obtained were very 
similar to those of Wille 1 : callus was seen in the sieve-tubes of the 
medulla, but no secondary sieve-tubes were demonstrated. 
Nereocystis Luetkeana , P. and R. Some spirit material was investi- 
gated, and the conditions obtaining in the sieve-tubes appeared to be very 
similar to those present in Macrocystis. In the primary pith filaments 
callus was found in large quantities, often entirely obliterating the lumen. 
In the young secondary sieve-plates callus was seen in surface view to 
appear in patches as in Macrocystis ; in older stages it was seen to accumu- 
late in masses, at first as in L. saccharina. Soon, however, it became 
heaped up in the centre by deposition from the dense central mass of proto- 
plasm, and then spread over the whole sieve-plate, forming a large cushion. 
In a few old sieve-tubes callus was seen to be formed throughout the 
length of the tube, and stages like that seen in Fig. 23, PI. XIX, were 
observed, in which there could be no doubt that the callus was deposited 
by the protoplasm. 
VIII. Summary and Conclusions. 
I. There can be no doubt that the ‘ trumpet hyphae ’ in Macrocystis 
pyrifera and Laminaria saccharina are to be looked upon as true sieve- 
tubes. They represent the modified, original central cells of the thallus, 
and may be termed ‘ primary pith filaments ’. Though they differ as to 
their degree of development, they are certainly homologous with the 
secondary sieve-tubes of Macrocystis , which are similarly derived from the 
modified primary cortex of the young thallus. 
II. Secondary sieve-tubes have also been demonstrated in Laminaria 
saccharina and are probably present in Laminaria digitata. These, like the 
secondary sieve-tubes in Macrocystis , represent the whole of the original 
1 Wille, 1 . c., 1897. 
