FERN CROSSING AND HYBRIDIZING 35 
chapter on the Life History of a Fern, a small green scale. On the 
under side of this, two sets of organs, male and female, are formed, 
while at the base of the latter an embryo seed lies embedded. 
When mature a number of antherozoids, tiny motile bodies pro- 
vided with cilia, swim in the dewdrop beneath the scale to the 
archegonium under which the embedded seed lies, and by passing 
into this effect the fertilizing process. Now it is obvious that 
normally there is practically no chance of an antherozoid crossing 
the comparatively wide gap which lies between one prothallus or 
scale and another, and although it has been mooted by Mr. Lowe, 
and is indeed quite probable, that minute insects like the Podura or 
Skipjack and others may convey antherozoids from one prothallus 
to another, this obviously cannot be profited by for systematic 
crossings, and hence other methods are adopted. The microscopic 
character of the spores creates an initial difficulty in sowing since 
it is essential, so far as practicable, to know what is being sown, 
and it is in the experience of all Fern-raisers that stray spores, shed 
and scattered broadcast from other Ferns, are apt to develop in 
conjunction with the desired ones and thus introduce an uncertain 
factor into the experiments. To avoid this, spores should be 
collected as soon as ripe and as early as possible in the season, thus 
reducing this risk toa minimum. Having secured as far as possible 
a pure sowing of each kind intended to be crossed and taken the 
precautions mentioned in our chapter on Propagation, the two 
kinds should be thoroughly mixed and sown rather more thickly 
than usual, so as to ensure close proximity of the resulting pro- 
thalli, or they may be sown separately, each on relatively thinner 
lines, the one after the other. Here it may be remarked that some 
spores germinate and develop far more rapidly than others, and in 
that case two separate sowings at relatively distant periods may 
be made, the slower germinator first and the faster later on. Which 
is which can only be determined by experience, and the above 
remark applies mainly to hybridizing where different species are 
concerned ; with varieties of the same species it may be ignored. 
The prothalli having reached full size, the time will have arrived 
for facilitating the transference of the antherozoids of one pro- 
thallus to another. These antherozoids have a free - swimming 
period, and then make their way to the archegonia. Clearly if at 
this time we can judiciously flood the prothalli, there is a fair 
chance of a general distribution of the fertilizing antherozoids, and 
that the chances of cross alliances are greatly increased. Lowering 
the pot or pan very gently into warm water until this percolates 
from below and just bathes the prothalli without entirely sub- 
merging them gives this chance, time, say half an hour, being 
afforded for the stimulus of the warmth to rupture the antheridia 
and launch the contained antherozoids upon their wedding trip. 
As a theoretical possibility the following plan has been advanced. 



















