302 GAMETOPHYTE OF BOTRYCHIUM 



is interesting to note in a closely allied order occurring in the 

 tropics, that the sporangia are developed directly upon the leaves 

 (Fig. 217) instead of upon special branches and that they are 

 sometimes associated together in groups, known as sori (sing, 

 sorus) and provided with thickened cells, the annulus — charac- 

 ters that will become conspicuous in the next order. These 

 sporangia originate, however, as in Ophioglossum and open by 

 transverse clefts which operation is promoted by the unequal 

 drying of the thick- and thin-walled cells of the annulate forms. 

 (a) The Gametophyte. — The gametophyte or sexual genera- 

 tion is not often met with, owing to the fact that, like the sporo- 

 phyte, its development is associated with mycorrhizal fungi and 

 consequently it is usually completely buried in the soil and usually 

 quite devoid of chlorophyll. The various stages in the germina- 

 tion of the spores have never been observed, but the mature gam- 

 etophyte of Botrychium was found a few years ago by Jefifrey 

 and carefully studied. It appeared as a rather tuberous body 

 that is provided with numerous rhizoids and a growing apical 

 cell as in the Bryophyta (Fig. 218, A, B). The archegonia and 

 antheridia are usually borne upon the upper surface of the game- 

 tophyte and in origin and appearance are rather suggestive of 

 Anthoceros. The antheridia consist of a number of mother cells 

 quite buried in the tissues of the thallus, being covered by one 

 or two layers of cells which are destroyed or break open when 

 the male gametes are mature (Fig. 218, C). These gametes are 

 quite different from any yet seen, being spirally coiled and pro- 

 vided with numerous cilia (Fig. 218, D). The archegonia are 

 similar to those noted in Anthoceros, consisting of a rather short 

 neck with two central canal cells and a swollen base sunken in 

 the tissues of the gametophyte (Fig. 218, £). The female gamete 

 is formed at the base of the canal cells which finally become 

 mucilaginous and thus form an open passage-way for the entrance 

 of the male gametes as soon as the lip cells have opened. It has 

 been shown in the common ferns that malic acid is present in 

 this mucilaginous substance which strongly attracts the male 

 gametes so that they crowd into the canal, often completely chok- 

 ing it. So we see that the gametophyte of this fern (though 



