24 Address of the President. 
vegetable and animal life, I shall first proceed to inquire how 
far these researches tend to modify our idea of what consti- 
.tutes a cell ; and shall then test these modifications by the 
results of inquiries into the structure and development of 
more complex organisms. 
The typical vegetable cell has commonly been considered 
to consist, externally, of the cellulose wall, — next to this, of 
the primordial utricle, — within this, of a layer of protoplasm, 
usually mingled with chlorophyll-granules, — and, finally, of 
the liquid cell-contents. But we find, among the simplest 
Protophytes, that all the functions of vegetative life are per- 
formed by beings which do not present any such differentia- 
tion of parts. Thus each individual of the Palmoglcea 
macrococca (Kutzing) seems to be a particle of viscid plasma 
containing green granules, having neither definite limitary 
membrane on its surface, nor definite cavity in its interior ; 
and this is surrounded by an indefinite gelatinous envelope, 
which usually coalesces with that of other similar particles, 
so as to form a continuous slimy matrix. Now each of these 
particles has a nucleus like that of fully-developed cells ; it 
increases by drawing into itself nutritive materials, which it 
converts into the organic compounds it requires for its aug- 
mentation ; it undergoes duplicative subdivision, by which 
the single particle gives origin successively to two, four, eight, 
&c., after the ordinary method of multiplication of unicellular 
plants ; and finally it conjugates with another like itself, the 
substance of the two particles being fused together in such a 
manner as to demonstrate the non-intervention of any limitary 
membrane, and the product being a " spore" or rather a pri- 
mordial cell," which originates a new generation by the re- 
newal of the process of duplicative subdivision. 
Now if we compare the life-history of this Palmoglcea with 
that of any unicellular plant that may be familiar to us, — one 
of the DesmidiacecB for example, — we shall see that in all 
essential particulars it is the same ; and that the only diff'er- 
ence lies in the less-developed condition of the former as com- 
pared with the latter. For if its nearly homogeneous mass of 
protoplasm were to take upon itself that tendency to differ- 
entiation of its component parts, which operates in the pro- 
duction of the perfectly-developed vegetable cell, a very easy 
transition would speedily manifest itself from one condition 
to the other. For the surface of the protoplasm would gradu- 
ally undergo condensation, so as at last to be converted into a 
more or less definite membrane, the " primordial utricle * 
* It is maintained by some recent observers, that the " primordial 
utricle" of Mohl is not to be regarded as a proper membrane, because it is 
