248 SUMMARY OF CURRENT RESEARCHES RELATING TO 



their classification and arrangement need not be very diflferent from 

 those accepted for other portions of the vegetable kingdom. It would 

 seem that with as much propriety one might consider the number of 

 granules on a Staiirastrum, or striae on the frond of a Closterium, of 

 specific importance ; or the number of fibres in a given space of a 

 specimen of pine or oak, of value in determination of species. I 

 venture the assertion, that if one were to show to the distinguished 

 microscopist who has advocated this view of the importance of fineness 

 of striation, a slide of diatoms, and request him to say what they were, 

 he would name them all, correctly too, and never once resort to 

 measurement of striation to do so. Now, if this can be done, and it 

 is done every day by experienced microscopists, what is the necessity 

 of bringing in an element which most students of the Diatomacese 

 consider very variable and exceedingly difficult to determine. I would 

 not have it understood, by what I have said, that I consider striation 

 as of no importance ; in conjunction with other things, it has a certain 

 value, but at best only secondary. 



" I do not suppose that Count Castracane would for a moment 

 assert that Stauroneis Phoenicenteron, e. g., has the same number of 

 strias in ' 001 of an inch as Stauroneis gracilis, and yet I have fre- 

 quently found the latter conjugating, and the sporangial frustule 

 is S. Phoenicenteron. The sporangial frustules of the diatoms are 

 notoriously more coarsely marked than the parent frustules. There 

 are a great many species of diatoms, belonging to the N. prima group, 

 which really pass into each other so gradually that, even by the help 

 of striation, it is difficult to distinguish them ; N. affinis produces, by 

 conjugation, true N. prima, and I have even observed the large frus- 

 tules of the latter again producing monsters, by conjugation, far more 

 coarsely marked than the parent frustules. Shall we consider the 

 sporangial form as one species, and the parent form another ? 



" I have before me now a slide of Gomplionema olivaceum containing 

 myriads of frustules, many conjugating, and some with the parent 

 frustules yet adhering to the sporangium. The comparative striation, 

 as measured with a Powell and Lealand spider-line micrometer, is very 

 nearly as 4 to 6, and as the individual measurements of the parent 

 frustules give for the striation 28 to 30 in • 001 inch, we have for the 

 sporangial ones say about 20 in "001 inch. In this gathering there 

 are numerous free sporangial frustules wholly formed, and quite as 

 coarsely marked, and apparently numerous others of intermediate 

 size and striation. Of what value would striation be here ? What I 

 have said about G. olivaceum is equally true of other diatoms, notably 

 of the genus Cymhella. And yet in conjunction with other characters 

 the striation should not be ignored. In the same gathering, on 

 Isthmia enervis, the striation may be so nearly the same on larger and 

 smaller frustules as to appear to be of specific value ; but it by no 

 means follows that it will be the same in this species from a widely 

 different locality, nor does my experience with Eulenstein's prepara- 

 tions of Isthmia enervis coincide with that of Count Castracane. I 

 find that the small granules on the connecting zone, or central 

 portion, say in ■QOl inch, in the ratio of about 5 to 7, measuring, 



