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 to a 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. 



