~ four next the front margin of the 
230 
THE DICTIONARY OF GARDENING, 
Prothallus, or Prothallium—continued. 
sub-divided by cell walls. The result is that a structure 
is formed in the shape of a flask with a long, narrow 
neck. The hollow of the flask is occupied by a large 
Fic, 295, IMMATURE ARCHEGONIUM, much magnified, — n, Neck- 
cells; e, Canal, still closed above, and filled by the Canal- 
cell; 0, Oosphere ; e, e, Epidermis of Prothallus, 
cell, the oosphere, rich in protoplasm (see Fig. 295). The 
tube of the neck is at first filled with a narrow cell, 
the canal-cell, the cell wall of which becomes muci- 
laginous, swells, and is expelled from the outer opening 
of the tube, leaving a passage for the antherozoid down 
the tube to the oosphere, when the latter is ripe to be 
e 
FiG. 296. LONGITUDINAL SECTION OF MATURE ARCHEGONIUM OF 
FERN, much magnitied—n, Neck-cells ; e, ing of Canal 
down neck; 0, Oosphere; e, e, Epidermis of us. 
acted on by it (see Fig. 296). The antherozoids are caught 
in the mucilage while moving over the moist Prothallus ; ° 
they wriggle down the tube, reach the oosphere, and 
fertilise it. The latter very soon begins to grow; and the 
final result is the development of the oospore into the 
leafy plant or Fern. It may be mentioned that the 
F1G. 297. DIAGRAMMATIC SKETCH OF CONNECTION oF YOUNG 
FERN WITH PROTHALLUS—p, Prothallus; rh, Root-hairs of 
—— si A Foo ag soe — — in hollow of 
— — » @; fr, Very ee 
oospore, at a very early period, divides into ei ht cells. 
in two layers. Of these cells, four lie next a ie and 
latter, the two farthest from the neck of the archegonium 
give origin to the first leaf or frond; one, near the neck 
to the growing point of the stem; and the fourth to hairs. 
of the other four cells, one, opposite to the stem, de- 
velops into the root, one ultimately disappears, and the 
other two form the “foot,” a structure that remains sunk 
in the archegonium, which has grown so as still to sur- 
round the foot (see Figs. 297 and 298). By means of this 
w 
| Trregularly-lobed masses of cellular tissue, 
` trace of 
Prothallus, or Prothallium—continued. 
organ, the young plant absorbs nourishment from the 
Prothallus, which, for a time, increases in size, but is 
gradually used up, and withers away, and afterwards 
the young Fern is able to nourish itself by its own 
roots and leaves. 
FiG. 298. YOUNG FERN GROWING FROM PROTHALLUS, slightly 
enlarged—p, Lower Surface of Prothallus ; rh, Root-hairs of 
Prothallus; fr, Young Frond of Fern; r, Root of Fern. 
Two departures from this mode of reproduction have 
been detected in Ferns within recent years. The one 
of these, called “apogamy” (from apo, afar, and gamos, 
marriage) by Professor de Bary, was detected, in Pteris 
cretica, by Professor Farlow, and is now known to occur 
in a few other Ferns, including Nephrodium Filiz-mas 
eristatum. In this process, the young Fern is produced 
as a bud from certain parts of the Prothallus, without 
the formation of sexual organs. The sexual process in 
this case is abolished, as the name indicates. 
In 1884, Mr. Druery stated, in the Linnean Society, 
the discovery that, in certain Ferns, the Prothalli are 
produced as outgrowths from the pinnules of the Fern 
fronds, and not from the spores. This process has been 
called “apospory” (from apo, afar, and spora, a spore or 
seed). It has been investigated and described by Pro- 
fessor Bower in examples supplied by Mr. Druery, of 
Athyrium Piliz-femina clarissima, and Polystichum an- 
gulare pulcherrimum. In this departure, the produc- 
tion of spores is suppressed; the Prothalli in the former 
ing modified sporangia, while, in the latter Fern, no 
the sporangium even can be detected. The 
sexual reproduction is not affected, and the leafy Ferns 
are developed from the Prothalli in the usual way. 
Though of very great scientific interest, the develop- 
ment of Prothalli, and of the sexual organs on them, is 
of less practical importance to gardeners in the other 
groups of Vascular Cryptogams than it is in the true 
Ferns; but an outline of the chief points of difference 
inthese groups may be given. In the small group 
Ophioglossew, represented in the British Flora by the 
Moonwort and Adder’s Tongue Ferns, the Prothallus is 
formed underground, is destitute of chlorophyll, and 
is usually formed of a mass of cells. It produces sexual 
organs, which resemble those of Ferns in the main. The 
Equisetinee, or Horsetails, resemble Ferns in the Pro- 
thalli being green, 
damp surfaces; 
gonia. * fhe former are produced near the tips of the 
lobes of the male Prothalli; the latter usually in the 
clefts between the fleshy lobes of the female Prothalli. 
- much 
So far as is known, their Prothalli — 
— 
