18 BRITISH FERNS 



2. That, given a prothallus, the fern might be produced by the 

 aid of a sexual bud, formed in the same place on the scale as a 

 sexual one, instead of by the normal interaction between anthero- 

 zoids and archegonial seed embryo, and thus eliminate both of 

 these (apogamy, previously discovered by Prof. Farlow). 



3. That the prothallus itself was capable of bearing spores, so 

 that the frond-forming generation was eliminated, and given the 

 power of these spores to perfect and produce offspring of like 

 capacity, the frond stage of the fern itself, as we know it, might be 

 replaced by a minute Marchantia-like growth of small green scales, 

 a reversion, in fact, to one of the primary forms of vegetation. 

 This fact was demonstrated by Dr. Lang, 1 but so far these prothallial 

 spores have not germinated. 



4. As regards the elimination of the prothallus, this is evidenced 

 by innumerable cases of bud or bulbil reproduction, by which 

 young plants are produced by excrescent growths on the fronds 

 and elsewhere, such as we see in the familiar Asplenium bulbiferum 

 in which the fronds are profusely dotted with young plants. 



To illustrate these various short cuts we reproduce Professor 

 F. O. Bower's diagrams in Fig. 8 ; but it must be borne in mind 

 that all these peculiar vagaries have been noted in connection 

 with varietal forms of Ferns, that is, such as present marked diver- 

 gencies from the ordinary form of frond, which has led to special 

 study of their behaviour in the prothallus stage, with these re- 

 markable results. It is therefore seen that the life cycle of a Fern 

 is not only more complicated than that of a flowering plant, but 

 that it is capable of being varied in so many ways, that every 

 individual phase of the normal process may be omitted and repro- 

 duction yet be successfully effected. 



Finally, our description of the Life History would be incomplete 

 did we omit a reference to the wonderful arrangement by which the 

 spores are scattered when ripe. On examining the heaps of spore 

 capsules, we shall find them in most species — the exceptions we 

 may ignore — to be beautiful oval, shining brown bodies, supported 

 on short ribbed stalks, and that these ribs extend right over the top 

 of the capsule, like the ridge of a fireman's helmet, only stopping 

 half-way down the opposite side (Fig. 2). When the spores are 

 ripe, this ribbed portion contracts, and eventually exercises such a 

 strain that a crack appears at the point where it ceases ; this slowly 

 widens, exposing some of the spores, and after a wider and wider 

 yawn, the whole of the top flies back with such violence as to jerk 

 the spores in all directions. A tiny pinch of capsules, placed on a 

 glass slip and watched under a microscope in a warm room, is a 



: - : W. II. Lang, M.B., B.sc, on "Apogamy and the Development of Sporangia 

 upon Fern Prothalli. Phil. Trans. Royal Society, vol. 190 (1898), pp. 187-228. 



