FILICINEAE LEPTOSPORANGIATAE 381 
great differences in the habit and structure of the sporophyte. The 
stem is sometimes a creeping rhizome, sometimes a stock which is 
closely covered by the bases of the leaves. Upon these the sporangia 
are borne. In the M. they are formed on the under side of ordinary 
foliage leaves, but in the O. the leaf divides some way above the base 
into a ventral spike bearing sporangia, and a dorsal * sterile ’ portion 
or green blade. The sporangia also differ in the two orders [q.vfi 
Both are homosporous. 
Classification : 
Order i. Ophioglossaceae : sporangia on special spike, borne on 
ventral side of leaf. 
2. Marattiaceae : sporangia on ordinary foliage leaves, 
usually combined into synangia. 
To these various authors, e.g. Campbell (loc. cit.), add the Isoe - 
taceae as a heterosporous group. In this work they are treated as 
belonging to Lycopodineae, but their systematic position is exceed- 
ingly doubtful. 
Filicineae Leptosporangiatae. [See above for relationship to other F.] 
We shall deal with the two groups separately. 
1. Homosporous F. L. These plants are generally known as 
Ferns; only a few of the other groups of F. come in popular estima- 
tion under this title. An outline of the general life history will be 
found under Pteridophyta, but a few details must be added here. 
The fertilised ovum on the prothallus developes directly and with- 
out any resting period into a fern-plant. There is no intermediate 
period of rest as there is in flowering plants when the seed is ripe. 
The prothallus continues to assimilate food and supply the young fern 
until the latter is able to do so for itself. The primary root remains 
small or withers away, and new ones are adventitiously formed from 
the stem or from the leaf bases, as the plant continues to grow. The 
mature plant may be of almost any size from the tiny filmy ferns 
(Hymenophyllum) to the large tree ferns [eg. Cyathea, Alsophila). 
The stem grows by an apical cell, 2- or 3-sided, cutting off segments 
on each face alternately. From these segments by further divisions 
arise the tissues and members of the plant. The leaves form a little 
way behind the growing apex as in flowering plants. One segment 
(but not every one) gives one leaf : the leaf grows by an apical cell 
also. The stem may be erect, or may climb (as in many epiphytes), or 
creep on the surface, or below it as a rhizome. Its growth is slow 
and branching infrequent. The leaves are borne upon it, the inter- 
nodes being as a rule short in erect, long in creeping stems. The 
phyllotaxy is not so definite as in flowering plants, but the leaves are 
very commonly in ranks or straight lines dependent on the position 
of the segments cut off from the apical cell of the stem. The lateral 
buds arise either on the leaf (as in Nephrodium) or on the stem; in 
the latter case they are rarely axillary, but usually beside the leaf. 
