OF FERNS FROM THEIR SPORES. 119 
elongated in like manner and again divided, and sometimes this goes on until a row of 
five or six cells is formed (figs. 3 & 4): when the first cell grows out into a long filament, 
fewer cells are formed in the simple row. Chlorophyll granules show themselves, in- 
creasing in quantity in the newly-formed parts. The first formation of radical fibres often 
occurs in the earliest stages, consisting in the growth outward of the wall of one or more 
of the cells of the filamentous prothallium into a slender tube, which attains a great 
length, remaining narrow and uniform in diameter, and never having its cavity cut up by 
partitions. All the roots met with on full-grown prothallia exhibit the same characters ; 
they are tubular prolongations from the inferior walls of cells of the green, vegetating, 
frondose expansion, and their tubular cavities are freely open into those of the cells from 
which they arise. | 
After a time the youngest cell of the growing prothallium becomes more expanded in 
the transverse diameter, and after the next transverse subdivision of the cavity we find a 
new mode of increase, namely, a division of the newest cell in a direction parallel to the 
original direction of growth; by the frequent repetition of these two modes of extension 
the prothallium gradually acquires a somewhat three-sided figure, with the angles rounded 
off (figs. 5, 6 & 7). When it has attained a certain size a difference begins to present itself 
in the degree of expansion of the new cells continually formed by subdivision; those in 
the middle of the front border (that directly opposite to the original point of growth) 
remain small and are greatly surpassed in size by those at the sides and at the two ante- 
rior angles, so that the latter advance forward as rounded lobes, leaving a notch or exca- 
vation in the middle, giving the entire prothallium the form which in leaves, &c. is termed 
obcordate (fig. 9). In the meantime great quantities of radical hairs are developed from 
the lower faces of the cells in the neighbourhood of the obtuse apex of the heart-shaped 
frond, that is, about the posterior part of the prothallium, which generally exhibits a very 
ill-defined margin, as the cells formed at first often decay away and disappear, leaving a 
ragged edge (figs. 9 & 10). 
While the ga pas which varies a good deal in different species in the lateral p 
pansion of the two lobes, is becoming perfected, the middle and posterior region of the 
prothallium, near where the roots arise, begins to display a new mode of growth. Up to 
this time the entire prothallium consists of a single flat layer of cells, in which state the 
lateral lobes and the anterior border persist, but in the central and posterior p the 
cells now become divided by horizontal walls, so as to give the prothallium a thickness 
of two, three, or more cells in the vertical section (figs. 62 & 67). The thickened portion 
forms a rounded cushion-like projection from the inferior face of the prothaliewn (fig. 51), 
while the upper surface remains flat or is even slightly depressed in the region over the 
thi ing. | | | : 
rigide presented by the cells are as follows :——their walls are delicate and closely 
à aul : between them; they are lined by a 
1n apposition, so as to leave no intercellular Fr. bat fad ilie is 
layer of mucilaginous consistence (the primordial utricle) enclosing a og » fa ng 
cavity of the cell. This substance is coagulated and contracted by acids and iodine, so as 
to collect all the cell-contents into an isolated mass in the centre. In the cell are also 
found, more or less abundant, chlorophyll globules, some imbedded in the meque 
; R 
