50 ON THE GENERA ANADYOMENE AND MICRODICTYON. 
the disk of the frond and the main stems than there is between the cells 
in Anadyomene, which is, as it were, all composed of numerous di- 
verging cells only differing in size. 
The cells on the upper part of the sides of the main series in Ana- 
dyomene are furnished with a series of rather large cells placed at right 
angles with them; there are only a very few very small cells so placed 
n Grayemma, and they are not to be seen except in a few places on the 
frond. 
If the chain of cells of the two genera are compared, it will be found 
that in Anadyomene each cell gives off at the tip a radiating series of 
cells, some of which being larger than the rest form a branch which at 
its apex again gives off a radiating group of cells, some of which are 
similarly elongated and are proliferous, so that the frond is composed of 
a succession of trifid and in some rare instances four- or more nume- 
rously-divided branches. In Grayemma, on the contrary, the series of 
vells remain unbranched as long as they are parallel, and after being 
parallel for a time some diverge to the left or to the right, and then 
form another stem, giving off diverging series of cells. 
Grayemma the midribs extend almost up to the edge of the 
frond with a single group of cells, forming a fan at the top quite 
close to the edge, which is very different from the structure seen in 
Anadyomene. 
All the midribs and branches of the specimens I have been able to 
examine are formed of several parallel close series of cells, except the 
tips of some of the smaller branchlets, which consist of a series of two or 
three cells placed one on the other, and ending in cells diverging from 
the tip of the last one like a fan, except in two cases, one a slender 
branch, which starts from the midrib and extends to the margin ; this 
branch consists of a single series of cells as in Anadyomene, about twice 
s long as they are broad ; and only giving off a short single branch, 
not dividing into branchlets as in Anadyomene. The second example 
of a single series of cells occurs in a simple branch that runs parallel 
_ to the main stem, and at length becomes united to it, and then assumes 
a compound form. This branch can only be considered as a series of 
Mitta thai h Nain ae ce ee DC rae Ges t m . 
.. celis that ha y om its proper position in the 
.. growth of the plant, and assumes it again, but it shows that the main 
stems are composed of many single series of cells united into a bundle 
