34 
CORRESPONDENCE. 
spurious lines alluded to by Dr. Woodward, wliicli some persons have 
nicknamed " ghost lines." As the frustule was already lying vertical, 
I had merely to move it about an inch and a half to the (apparently) 
left side of the objective. 
Fortunately, the dispute — if there be any dispute — is one that can 
be easily settled. Either Dr. Woodward may forward a letter to 
Herr Seibert, " Optisches Institut, Wetzlar," — and from my know- 
ledge of Herr Seibert's obliging disposition I am sure he will readily 
send him a copy of the photographs shown to me, — oi, if Dr. Wood- 
ward prefer it, I will forward to Mr. Lealand (of the firm of " Powell 
and Lealand ") the slide I showed to Dr. Eabenhorst ; and then, if 
Mr. Lealand cannot see the longitudinal lines, the case is ended. 
I may as well mention at once that my collection of Frustulia 
Saxonicas, which is a pretty extensive one, ranges from specimens 
having lines closer and finer than those in Amjphijpleura pellucida to 
such as exhibit lines as coarse and strongly marked as those in 
Mr. Norman's NitzscMa sigmoidea. Thanks to Dr. Schumann's admi- 
rable pamphlet, we now know that this great diversity in the same 
species depends on dilferences of elevation of the diatom's habitat, 
that is, on differences of temperature, inasmuch as there is a fall 
of one degree of Eeaumur for every 600 feet of elevation above the sea 
level. He further tells us (pp. 7, 17) that he found Frustulia 
Saxonica at various elevations, from 4000 to 6454 feet above the sea 
level. See also pp. 85, 93. 
One word more about slides. Many a man fancies he has got a 
bad glass when he has really got a bad slide. There are slides and 
slides; and, unfortunately, the bad ones are in a terrible majority, 
as bad things usually are. Something of this sort has been at the 
bottom of Dr. Woodward's (reported) failure. If he is rightly reported 
as having failed, my explanation is, that he failed where everyone 
else would have failed, and has merely been wasting his time on a 
bad slide. 
I am the more inclined to adopt this view from Dr. Woodward's 
mention of MoUer; for I hardly need say that MoUer, in the matter 
of test-diatoms, is the very worst guide anyone could possibly take. 
He seems indeed not to have the slightest idea that any test-diatom 
can require for its resolution any position other than horizontal 
or vertical. It is also notorious that, if a customer applies to him for 
Navicula crassinervis, he sends Frustulia Saxonica labelled " Navicula 
crassinervis " ; and if the customer wants Frustulia Saxonica he sends 
it labelled " Frustulia Saxonica." Wrong naming seems to be his 
speciality. 
It is quite true that Dr. Schumann * says (in which point I do not 
agree with him): "Frustulia Saxonica Eabenh. Alg. p. 227. It 
appears in the following forms : — 
"1. Nav. crassinervis Breb. Syn. I. p. 47. xxi. 271. Beitr. p. 10, 
11, 13 c. 
" 2. Nav. cuspidata Ktz. Syn. xvi. 131. Beitr. II, 16 a." 
But to say that Frustulia Saxonica has as its sub-species Nav. crassi- 
* ' Die Diatomeon der holien Tatm,' p. 79. 
