Fertilization of the F loridee. 5 
In any subsequent division of the cell, by which, as already 
mentioned, marginal cells alone are always separated, this 
pit never occurs in any such marginal cell, but is always pre- 
served in the joint-cell itself. The same thing is repeated at 
each cutting off of a marginal cell, so that from the number 
and distribution of these pits, even in the quite unequally 
extended cells of full-grown branches of the thallus, the 
genetic connexion of the individual cells with the whole of 
their neighbour-cells may be recognized, at all events so long 
as the occurrence of secondary pits does not produce difficul- 
ties. Such secondary pits, however, frequently occur, especi- 
ally in species with a small-celled thallus, developed in such 
a manner that the individual thallus-cells are placed in con- 
nexion with all the neighbouring cells by subsequent develop- 
ment of one or more pits in the separating septa, indifferently 
whether they are or are not separated by these septa from 
sister-cells. Nay, even the cells of the secondary rhizoidiform 
medullary-filaments of the thicker Floridean stems are some- 
times brought into close connexion with individual cells of the 
tissue through which they grow, by such secondary pits. 
These pits (which are generally circular) are closed by ex- 
tremely thin membranous lamellz. But on each side of these 
closing membranes there always lies a thick lamina of a very 
dense substance (very easily and intensely coloured* by heema- 
toxyline and analogous staining materials), and this so closely 
and firmly that it can rarely be separated, and only by swel- 
ling up of the closing membraneyt. ‘The two plates are 
walls runs the organic longitudinal axis of the joint-cell. As already 
stated, no transverse division nor any (organically) median longitudinal 
division ever occurs in a joint-cell, and consequently no dissepiment is 
ever formed in the joint-cells which either cuts their organic longitudinal 
axis or includes it; hence it follows that the joint-cell must always retain 
the two original pits in the two end-surfaces, as indeed is the case. 
* With regard to this behaviour with colouring agents the substance of 
these closing plates of the pits shows a very close analogy with the so- 
called mucilage of the sieve-tubes,’which, however, I think, onthe ground 
of repeated investigations (on Cucurbitacez), must be regarded quite 
otherwise than is now commonly the case. 
Thus, while this mucilage is generally regarded as lifeless, and supposed 
to travel in the sieve-tubes from cell to cell, I am quite unable to find 
in the facts any support for such a migration of the mucilage. In my 
judgment this “ mucilage ” rather remains In a definite form (which, how- 
ever, is exceedingly easily destroyed in preparation) in the individual cells 
in which it was produced. In the more complicated cases (¢. g. 1m the 
Cucurbitacez) the formed mucilage-masses (closing plates of the sieve- 
plates and uniting hollow cylindrical cords) of the individual joints of the 
sieve-tubes (cells) all remain in connexion with each other, and thus 
form in the plant a connected system of peculiar cords. 
+ I succeeded in effecting this in a very instructive manner In speci- 
