3 1 6 Sykes.— -A natomy and Histology of Macrocyst is pyrifera and 
V. Sieve-plate Development and Callus Formation in 
Macrocystis and Laminaria. 
In this section I wish first to point out how completely the observed 
series of changes in the development of the sieve-plate in these two plants 
harmonizes with the interpretation of sieve-plate development in Pinus 
given by Hill . 1 From these researches it appears probable that the boring- 
out of the protoplasmic threads to form slime-strings is due to ferment 
action. In Macrocystis and Laminaria , after the manner described for 
Pinus , the passage of the ferment down the young threads may be traced 
by the alteration of the staining properties of the protoplasm and by the 
change of the cell-wall into callus. It appears in Macrocystis 2 , as in Pinus 3 , 
that the ferment produced in any given sieve-tube is only able to act as 
far as the middle lamella of the wall which separates this sieve-tube from 
an adjoining one, a fact which lends support to the view that the young 
threads are interrupted at the middle lamella . 4 Structures which may be 
compared to the median node of the threads of Pinus and to the median 
nodules of the slime-strings in that plant 5 were occasionally met with in 
Macrocystis 6 , and might have been more distinctly seen in better preserved 
material. 
The various states of callus found occurring in Laminaria saccharina 7 
confirm the idea that that substance is a hydrated form of cellulose, and it 
is suggested that it is in a different degree of hydration in each of the 
states described. In summer there is present in the sieve-tubes a substance 
which will not react to any known callus-stain, but by hydration with 
swelling reagents it is possible to induce it to stain with London blue. 
Further swelling of callus which stains naturally with London blue causes 
it to stain more deeply with that reagent, but can never induce it artificially 
to attain a sufficient degree of hydration to stain with Water blue, though 
sometimes it can be made to react when treated with Russow’s callus 
reagent after swelling for a considerable period. In winter all degrees of 
hydration of the callus were found in the various elements of Laminaria. 
It appears that in the Laminariaceae, as in Phanerogams , 8 callus can 
originate either by a change in the already formed cell-wall or by deposition 
from the protoplasm ; in the formation of callus-rods in the sieve-plate it seems 
highly probable that the callus is produced by a change in the cell-wall. 
But with regard to the accumulation of callus in masses at the sieve- 
1 Hill, 1 . c., 1901, II, pp. 594-596. 3 Cf. Figs. 14, 15, PI. XIX. 
3 Hill, 1 . c., 1901, II, Figs. 18, 23, PI. XXXII. 
* Cf. Gardiner, Proc. Camb. Phil. Soc., xiv, 1907, p. 209. 
5 Hill, 1901, Fig. 12, PI. XXXII, and Fig. 20, PI. XXXIII. 6 Cf. p. 304. 
7 Cf. p.313. 
8 Hill, 1 . c., 1901 ; and Hill, Notes on the Histology of the Sieve-tubes in certain Angiosperms, 
Ann. of Bot., 1903, p. 267. 
