36 Notes on Diatomacez. aro A ha 
that of which I sent an account, and illustrating specimens to the 
late Dr. Walker-Arnott—and which has been noticed by Mr. F. 
Kitton, who examined my specimens, in ‘ Hardwicke’s Science 
Gossip’ for May, 1869 *—of the occurrence of what are usually 
considered two distinct species of Gomphonema, viz. G. capitatum 
and G. constrictum, both growing upon the same stipes or stalk! 
But this is not all. Since then I have made gatherings at the 
same place, and still find the above two forms growing upon the same 
stalk, and two others of totally different outline which appear also 
upon the same stipes. So that here we would have four hitherto 
considered distinct species arising from the same individual. I do 
not name the two last-mentioned forms, as I am in some doubt with 
regard to the names that have been applied to them. The question 
of what is the individual in the Diatomacee is again raised by the 
observance of these facts, as well as those I described in my “ Note 
on a point in the habits of the Diatomaceze and Desmidiacez,” read 
before the Boston Society of Natural History, January 8, 1868, 
and published in their ‘ Proceedings.’ t The specimens illustrating 
the remarkable mode of occurrence of the two forms of Gompho- 
nema which I sent to Dr. Arnott unfortunately did not arrive until 
after his death; but, speaking of my having so found them, he 
wrote to me in the last letter I received from him as follows. I 
feel that I am justified in publishing this extract, as it is of such 
importance ; and I also know, from what he wrote to me, that he 
himself would not object to my doing so were he still living. 
“Your discovery of Gomphonema constrictum and capitatum 
growing on the same stalk is interesting, if you are not deceived. 
When a Gomphonema spore grows on a weed, the stalk (which is 
merely the external mucus collected at the one end) is formed by 
the growing frustule. It is not the stalk (or m Schizonema, the 
tube) which produces the frustule, but the frustule which produces 
the stalk or tube. Then when the frustule self-divides, several are 
formed, either side by side, or each may project a new stalk; but 
seldom with much regularity. Now every frustule and valye 
arising from the same spore must be precisely alike, being all formed 
from the original frustule by repeated self-division; and as self- 
division merely repeats the same identical form or variety, it is not 
easy to understand how it is possible to have two varieties of form 
on the same stipes. If there be no mistake on your part, you will 
overturn all the present views of the production of new frustules 
and valves. It is more easy to suppose that a frustule from another 
stipes had become agglutinated to the stipes. But as you say you 
have sent some in a bottle, I will examine it with care when it 
arrives. Every spore may produce a different variety, but it is not 
easy to understand that the same spore, or stipes, can give rise to 
= AVolvtv.,.p. 109. t Vol. xi., p. 361. 
