March 11,1871.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
725 
diatoms are distinguished as having a siliceous en¬ 
velope ; they form, cell by cell, a deposit of silex, 
which often has markings of the most extraordinary 
beauty; and the variety of these diatoms, and the 
extraordinary beauty and delicacy of then’ organiza¬ 
tion, make them favourite objects of study with 
microscopists. Then again, there is one point in 
their structure which has been of very great value 
to microscopists, viz. that they furnish some of our 
very best test objects. Now the finding of a really 
good test object is a matter of very great importance 
in the breeding, if I may use the expression, of the 
best object-glasses ; for our manufacturers set them¬ 
selves to the improvement of object-glasses, just as 
breeders do to the improvement of racehorses or prize 
oxen or pigs. Their object is to produce the best 
glasses, just as a man tries to fatten a prize ox in the 
shortest possible space of time. The manufacturers 
of microscopes set themselves to make lenses that 
shall show certain test diatoms either better than any 
other lenses or with a lower magnifying power. 
Now, there is one thing that I must put you on your 
guard against, and that is the tendency to produc¬ 
ing diatom-resolvers, so to speak,—lenses that shall 
best resolve diatoms; but this deteriorates to a certain 
degree from the production of lenses that are most 
useful in actual physiological research. This is a 
doctrine I have been preaching for many years, 
and I now find it is generally accepted,—that the 
lenses which are best for resolving diatoms in virtue 
of their wide angle of aperture are not, generally 
speaking, the best for ordinary physiological work. 
Therefore, if you are going in for a microscope and 
for getting the higher class of lenses, you should 
always consider what you want; if you are going 
to study these diatoms, then you must get lenses of 
particular qualities, just as if you want to hunt or 
ride races you must have horses that are of different 
qualities from those you would use as ordinary 
carnage horses. This is a point not sufficiently un¬ 
derstood, and there is a great tendency amongst our 
makers to meet the wishes of those who desire these 
special lenses to resolve special diatoms, and to 
work them up so as to get out of a particular power 
results that really ought not to be expected from it. 
Every power, in my opinion, has its own particular 
attributes, and to attempt to make a lower power do 
the work of a higher is a great mistake. Every 
power should be adapted to do the best work of its 
kind, to do in the best manner the work for which it 
is properly suited. That null be found to be the 
case with well-corrected lenses of comparatively small 
angle of aperture. I mean small in comparison 
with the very wide angles that are now sought in 
powers from a quarter of an inch upwards.—I make 
these remarks because I really hope and believe that 
some of you will make the microscope an object of 
interest in that kind of recreation which we all of 
us require after the fatigues of business; and, as I 
said in the last lecture, I cannot imagine anything 
more grateful to the mind, and really more interest¬ 
ing to those who will acquire the knowdedge requi¬ 
site to give it that interest. These lenses of a mo¬ 
derate angle of aperture may be obtained at very 
much lower cost than these special lenses that are 
manufactured with the express view of resolving 
diatoms.—I have placed several specimens of these 
extremely beautiful forms under the microscope up¬ 
stairs. I will allude to them more particularly pre¬ 
sently, but I may say there is no doubt whatever 
they are plants. They have all the attributes of 
plants, for if we just take away this curious siliceous 
envelope, we have simply a vegetable cell. 
There is one very curious and interesting thing 
about them, namely, the fact of their conjugation. 
This was discovered by my friend Mr. Thwaites, 
whom I have the pleasure of reckoning one of my 
own early pupils, and who is now curator of the 
Botanic Gardens in Ceylon. It' was very much in 
consequence of my recommendation that he devoted 
himself with a microscope that we should scarcely 
look at, so poor was'it, certainly inferior to one which 
you can now get for T3 or T4, to the study of the 
lower tribes of plants in the neighbourhood of Bristol. 
He was rewarded by the discovery of this very cu¬ 
rious phenomenon, which is termed conjugation. I 
will show you what this means in some other tribes 
of plants. There is one of these filamentous Con ferva. 
Two filaments of this, lying side by side, put out 
little projections, these unite together, and the green 
matter passes entirely from the cells of one tube into 
those of the other, and then, after a time, it all aggre¬ 
gates together and forms this green mass which is 
liberated at last by the bursting of the cell that en¬ 
closes it. These, I believe, are true sexual products, 
and this conjugation I regard as the lowest form of a 
true generative process, the reunion of the contents 
of two cells. Here there is very little difference 
between the male and the female. You can scarcely 
see which is the male and which is the female. 
Sometimes the process takes place in a little bridge 
between the two; each discharges its contents into 
the little bridge, and there does not seem to be any 
definite difference between the one and the other. 
But then, on going a little higher, we find that what 
is discharged from the cell that empties itself com¬ 
pletely is not mere simple green matter, but is com¬ 
posed of little minute filaments, similar to the sper¬ 
matozoa of animals. These little green filaments 
are called antherozoids, and they take the place and 
perform the function of the pollen liberated from the 
anthers of flowering plants. They are called an¬ 
therozoids, because they are so much like the sper¬ 
matozoa of animals, -zoid being the termination ex¬ 
pressing likeness to an animal. That mode of con¬ 
jugation leads us towards the true sexuality of the 
higher Cryptogamia ; but the conjugation of Dia¬ 
toms is essentially similar to that of the conjugating 
Conferva. The variety in the forms of diatoms is very 
great, but their conjugation is always the result of the 
meeting or reunion of two cells; and sometimes the 
contents of one are entirely discharged into the 
other, and sometimes the contents of both cells are 
discharged and mix with each other, and then a 
new envelope forms around it. That discovery was 
a most important one in fixing our ideas as to the real 
character of these bodies, by shoving that they were 
as truly Vegetable as these filamentous Conferva , 
about the vegetable nature of which there is no 
question whatever. 
Now I will take you to a higher form of vegeta¬ 
tion, the Ferns, to show you what has been the 
remarkable result of microscopic study in throwing 
an entirely new light upon the sexuality of the 
Cryptogamia. You all know that from the time of 
Linnaeus the sexuality of flowering plants has been 
admitted, and that the pollen performs the function 
of the male, and that the apparatus containing the 
ovules is essentially the female part of the organiza¬ 
tion. But as to the Cryptogamia, the lower tribe of 
