532 The American Naturalist. [July, 
mation of auxospores without conjugation is the primitive 
method, although Murray’ holds that the formation of auxo- 
spores by conjugation is probably the original method, and 
that their formation without conjugation is the derived method. 
Wm. Smith” divided the Diatoms into two tribes in the first 
of which the frustules are free, and in the second imbedded in 
a gelatinousenvelope. Under the first tribe he makes five sub- 
tribes, depending upon the form of the connecting membrane 
and the relation of the frustules to each other. The second 
tribe he divided into four subtribes based on the form of the 
fronds. This arrangement seems not only extremely artificial 
but also very impractical. Nothing about Diatoms is more 
variable than the form of the fronds; and where it is at all con- 
stant, such a system places closely related genera far apart; for 
example, Cymbella and Encyonema, Nitzschia and Homæocladia 
are placed in separate tribes, while in structure they are very 
similar, the main difference being that in Encyonema and 
Homeocladia the frustules are arranged in rows, while in Cym- 
bella they are free or stipitate and in Nitzschia they are free. 
This method of classifying Diatoms may be likened to a separa- 
tion of Grasses into those forming a dense sod and those not 
forming a sod; or of Dicotyledons into those exuding a 
resinous fluid and those that do not. Wm. Smith places 
Gomphonema in his first tribe, that is, the one having no gela- 
tinous envelope; but some species of Gomphonema are-stipitate 
while others are enclosed in an amorphous mass of jelly. The 
latter species would have to be placed in his second tribe, thus 
dividing the genus. It would lead to even greater difficulty 
than this, for the same species is sometimes stipitate and some- 
times imbedded in a gelatinous envelope. 
Of all existing systems that of Paul Petit seems to approach 
° An Introduction to the Study of Seaweeds, p. 195, 1895. 
1 For a synopsis of Smith’s classification see Pritchard’s History of the Infus- 
oria, 191, fourth edition, 1861. 
^ Liste des Diatomées et des Desmidées observées dans les Environs de Paris 
precedée d’un essai de classification des Diatomées. Bull. Soc. Bot. France, tom. 
XXIII-XXIV, Paris, 1877. 
An Essay on the Classification of the Diatomacee translated by F. Kitton, 
Monthly Microscopical Journal and Transactions of the Royal Microscopical 
Society, XVIII, 1877, pp. 10, 65. 
ceen, in Schenk’s Handbuch der Botanik, Breslau, 1882. 
