6 
I. K0BIXS0H—THE DIATOMACEiE. 
attending this process, which may he regarded as more nearly 
allied to that prevailing in the higher forms of vegetable life, 
are, however, involved in much obscurity. 
These organisms are very widely distributed over the surface of 
the earth. They are to be found in all latitudes and under almost 
every condition of climate and temperature. They abound in 
arctic, tropical, and antarctic regions. In the Botanical Journal of 
the Linnean Society for September last was published an account 
of a gathering of fresh-water species found at or near Cape Sabine, 
situated in the arctic regions in latitude 78° 40' north. This 
gathering contained 30 distinct species, and in looking through the 
list I find that I have myself found at least 10 of them in our own 
locality. Some of the others, which are more characteristic of 
mountainous districts, I have also found abundantly in Switzerland 
and elsewhere. This affords a good illustration of the cosmo¬ 
politan character of many species. Prof. Smith states with refer¬ 
ence to three of these, which are to be found in abundance near 
Hertford, viz. Synedra radians, Pinnularia viridis, and Cocconema 
lanceolatum, that they have been found in gatherings from many 
parts of Europe; from Smyrna, Ceylon, the Sandwich Islands, Hew 
Zealand, and Hew York ; from the loftiest accessible points of the 
Himalayas in Asia, and of the Andes in America. Another form, 
Epithemia gibla, stated to be an inhabitant of the geysers of 
Iceland and the lakes of Switzerland, is to be found abundantly in 
the King’s Meads between Hertford and Ware. 
The Diatomacese are to be found in about equal abundance in 
salt water, in fresh water, and in brackish water. The marine 
forms are, however, never found in fresh water, nor are the fresh¬ 
water forms ever found in the sea, unless carried thither by the 
action of rivers or other causes. Certain forms are found almost 
exclusively in brackish water. 
In our own district the fresh-water forms abound in every river, 
stream, ditch, and pond, and the student need fear no lack of 
material for study. His difficulties are more likely to arise from a 
superabundance, from the great and perplexing varieties of form so 
constantly met with, and from the labour of reducing them to order 
and classification. The number and variety of species frequently 
found together in a very small space is a matter of much surprise. 
Thus a single drop of water may contain perhaps 20 different kinds 
naturally associated together and jostling each other in the struggle 
for life. 
Whether or no it be true as it is said that fleas have their little 
fleas I cannot say. I can, however, state that large diatoms have 
their little diatoms. It is by no means uncommon to see a large 
specimen well-nigh covered with a number of small ones affixed to 
it parasitically, or more correctly in a state of commensalism. I 
met with a curious illustration of this arrangement a few months 
ago in the case of a large Surirella which I found in the ditch by 
the Warren at Hertford, and which had to bear the burden of a 
large growth attached to it of a smaller form known as Odontidium 
parasiticum. 
