16.2 Mr. G. H. K. Tliwaites o/i the Diatomacea? ; 
tion, maintain an independent existence (analogous to that of 
the buds of the higher plant), retain all the functions necessary 
for this independent life and for the propagation of the species, 
and undergo no modification from their original form. The life 
of an individual Diatomaceous plant we may therefore consider 
to extend from the production of the sporangium to the period of 
the conjugation of the numerous frustules which have originated 
from it. 
Now, for the sake of comparison, let us analyse the higher 
plant : we find it to consist but of a repetition of similar parts 
and structure ; and by carrying the analysis still further we ascer- 
tain the whole to be a modification of cellular structure, and that 
this cellidar structure is the product of a continued fissiparous 
division commencing from the contents of the primordial cell — 
the earliest condition of the embryo. In fact, that the entire 
active vital part of the whole plant is but a diffusion, as it were, 
of the contents (the endochrome) of the primordial cell. This 
endochrome possesses an individuality — a character — which 
though not appreciable by our senses, would be found, were it 
in our power to analyse it, to be as defined as when, in its 
further development, it has assumed all the marked peculiarities 
of the species. The complicated development of the higher plant 
may be said to be the expression of the quality of the endochrome 
of its primordial cell, just as the simple development of the frus- 
tule of the Diatomaceous plant expresses the quality of its endo- 
chrome. If the foregoing is a correct view of the matter, it fol- 
lows that the sporangium of the Diatomaceous plant is the ana- 
logue of the primordial* cell of the flowering plant. 
\Ye may now proceed more particularly to the subject of con- 
jugation. In many of the Diatomacece it is seen that at a certain 
period of the development of the species a union of the endo- 
chromes of two distinct frustules seems necessary for the continued 
existence of the species as well as for its reproduction. The 
physiologist will endeavour to arrive at some probable explana- 
tion of the reason why this mixture of endochromes is necessary, 
and he will feel it difficult to come to any other conclusion than 
this : namely, that in each of the conjugating endochromes an 
essential element must to some extent, probably veiy trifling, be 
wanting, whilst another essential element is in excess, and that a 
mixture of such an endochrome with another similarly condi- 
tioned, except that the quantities of such respective elements are 
reversed, must take place in order to restore the equilibrium and 
enable the species to continue its existence. The circumstance of 
the mixed endochrome developing around itself a cell-wall pre- 
* Tbia must not be confounded with the “ primordial utricle ” of Molil. 
