36 ALTERNATING GENERATIONS . 
off against this, a remarkable power of recovery on the return of moisture 
after being dried up. The sexual organs are usually borne by the Moss- 
Plant at or near to the apex of its upward-growing branches. The result 
of fertilisation—here again carried out by spermatozoids motile through 
water—is the formation of the Moss-Fruit, or sporophyte, which is 
throughout life a mere appendage on the Moss-Plant. At first it is, 
like that of Aiea, completely enclosed by the venter of the archegonium 
(Fig. 20); but it soon shows apical growth and 
elongation: the venter is then ruptured trans- 
versely, and the sporogonium is exposed. As 
it elongates its base remains embedded in the 
tissue of the Moss-Plant: its apex is still 
covered by the upper part of the archegonial 
wall, the calyptra; but at ripeness this is shed, 
and the enlarged capsule on dehiscence is able 
freely to scatter its’ spores. After this the 
ephemeral sporophyte dies away. 
Comparing such a Moss with Azccia, the 
phases of the life-history correspond, but their 
elaboration is different: the thalloid gametophyte 
of Ricca is replaced by the upright leafy plant 
of Catharinea. The fertilisation is still dependent 
on fluid water, but its product is more complex: 
there is in Catharinea a distinction of apex and 
base, with localised apical growth; but the form 
is still relatively simple, the whole construction 
being on the radial type, without appendages. 
The spore-production is restricted to the upper 
region, and takes place in one continuous sac. 
The sporophyte is still borne and nourished 
Bterci20s throughout its life by the parent gametophyte ; 
anil Peon Be and ‘Sh, = it is able by its chlorophyll-containing cells 
arhicromal walk late Fgh © carry on photosynthesis in some degree, as 
an accessory to the supply derived from the 
parent. It has a ventilating system like that characteristic of aerial 
plants, while this is absent from the gametophyte. 
A comparison of such a Moss with a Lycopod shows a different 
balance of the two alternating generations. The gametophyte of Lyco- 
podium cernuum is shown in Fig. 21 as a somewhat massive structure, 
bearing lobes of chlorophyll-containing tissue above, which have sometimes 
been compared with the leaves of a Bryophyte: below it is attached by 
rhizoids to the soil. Like the Moss it is an independent organism capable 
of selfnourishment. It bears its sexual organs about the bases of the 
lobes, and is dependent upon external fluid water for its fertilisation. 
Notwithstanding its massive bulk it is without a ventilating system. The 
