1870.] 215 [Edwards. 



examined my specimens, in Hardwicke's Science Gossip for May, 

 1869, Vol. v, p. 109, — of the occurrence of what are usually consid- 

 ered 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 indi- 

 vidual in the Diatomaceas is again raised by the observance of these 

 facts, as well as those I described in my " Note on a point in the hab- 

 its of the Diatomaceae and Desmidiacea?," read before the Boston 

 Society of Natural History, January 8, 1868, and published in their 

 Proceedings, Vol. xi, p. 361. The specimens illustrating the remark- 

 able mode of occurrence of the two forms of Gomphonema 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 grow- 

 ing 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 in Schizonema, the tube) which pro- 

 duces the frustule, but the frustule which produces the stalk or tube. 

 Then Avhen the frustule self-divides, several are formed, either side 

 by side, or each may project a new stalk ; but seldom with much reg- 

 ularity. Now every frustule and valve, 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 possi- 

 ble 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 



