2i8 Johnson,— The Procarpinm and Fruit 
The spores arise simultaneously from procarpial and pla- 
cental cells, and by the time that they have begun to appear 
the pore is fully formed, and it is only in oblique sections 
through it that any trace of the trichogyne is obtained. The 
pore is formed schizogenetically, from within outwards, re- 
minding one both in mode and in direction of origin of the 
formation of the pore of a stoma. The fruit-cavity arising 
schizogenetically increases in size lysigenetically, at the ex- 
pense of the innermost layers of the fruit-sheath, the cells of 
which gradually lose their contents and undergo mucilaginous 
degeneration, the quantity of mucilage and the number of 
mucilage-threads of Thuret and Bornet increasing with the 
age of the fruit. Threads crossing the fruit-cavity, before any 
spores are formed, are often seen. These are not mucilage- 
threads, but the drawn-out ordinary floridean pit-connections 
of the cells which are separating to form the fruit-cavity. It 
is necessary to exercise care in order to avoid confounding 
these or the mucilage-threads with the trichogyne. 
The preceding necessarily somewhat disconnected observa- 
tions may be briefly and usefully summarised as follows, the 
order of statement corresponding as nearly as possible with 
the order of origin of the different structures : — The first ex- 
ternal indication of the formation of a procarpium is the pre- 
sence of a small swelling on the surface of a thallus-branch due 
to the repeated periclinal division of the outermost one or two 
layers of cortical cells. The swelling so formed consists of 
some twelve periclinal layers closely applied to one another, 
and with cells all alike, except at that point where the pro- 
carpium is subsequently found. Here, owing to the absence 
of periclinal division, there is one large cell full of rich granular 
contents. This cell, after periclinal division generally has 
ceased, divides near its apex, and gives off several marginal 
cells which arrange themselves as described (Fig. i). At the 
same time the fruit-cavity begins to arise schizogenetically 
the fruit-sheath (pericarp, involucre) and the placental cells 
now full of granular protoplasm are marked off. By the time 
that the fruit-cavity has appeared, the end of the apical cell of 
