Laminaria sac char ina. 
293 
grow in from the inner cortical layers and anastomose between the 
pith-tubes. 
The descriptions given by Rosenthal 1 and Will 2 of young plants of 
Macrocystis bear a remarkable resemblance to Setchell’s account of 
Sacchoriza , for in Macrocystis the original central cells also become 
stretched in the same way to form elongated filaments, and the number 
of these filaments is later added to from the inner ‘ cortical ’ cells. According 
to Rosenthal the formation of cross-connexions may take place in one of 
two ways. The first method is that noticed by Setchell in Sacchoriza , and 
consists in the pulling out of a pit canal, owing to the swelling of the longi- 
tudinal walls of the pith elements, and in the formation of cross walls in 
the canal thus produced. The second method, which is, he says, more 
common, begins by the formation of a lateral protuberance which grows 
out from the longitudinal wall of one cell, forming a true hypha-like 
outgrowth, and, after a shorter or longer period of wandering, makes 
a secondary connexion with some other cell, the two cells connected being 
either quite near together or at some distance from one another. 
A large number of hyphae also grow in from the inner cortical cells, 
and, wandering in the substance of the swollen middle lamellae of the cells 
of the medulla, are responsible for much of the later growth of that region. 
Setchell states that in Sacchoriza broken cross connexions can grow out 
and form hyphae, and he also thinks that some of the hyphae formed from 
the inner cortex may assume a longitudinal course in the pith, and hence 
resemble, except for their smaller diameter, the original pith filaments. 
From the various accounts it is uncertain whether the ingrowing hyphae 
ever form secondary connexions in the medulla. Rosenthal 3 and Oltmanns 4 
assert that they never do so, but always have free endings, and on the whole 
this appears to be the opinion of most authors except Will 5 and Wille 6 , 
who believe that new connexions may sometimes arise. 
ii. Growth in thickness. The method of increase in diameter in the 
stem of Macrocystis has been a difficult question to solve. It is known that 
in the Laminariaceae growth in thickness is entirely due to the outer layers 
of the cortex, which divide rapidly by tangential and radial divisions. The 
same kind of meristematic growth certainly does take place in Macrocystis , 
and it is principally to this method of cell division that Rosenthal ascribes 
the increase in thickness in that plant. He points out that, while in the 
young stem the width of the cortex is approximately equal to that of 
the pith, in the old stem it may be ten times as great. On the other hand 
there can be no doubt that the diameter of the pith in the old plant is much 
greater than in the young one, but as to the method by which it has been 
1 Rosenthal, 1 . c., 1890. 
3 Rosenthal, 1 . c., 1890. 
6 Will, 1 . c., 1884. 
2 Will, 1 . c., 1884. 
4 Oltmanns, 1 . c. 
6 Wille, 1 . c., 1885 and 1897. 
