PTERIDOPHYTA-LYCOPODIN^ 159 



The gametoi^liyte or prothallium {fig. 917,^) is oiily known in 

 the genus Lycopodium, and shows considerable variety of form. 

 In some species it is a small tuberous body, with a colourless base 

 from which root hairs sprmg and an apex which is divided into 

 several green lobes ; in others it is altogether tuberous. In other 

 species again it is larger and is a cylindrical branched body 

 bearing gametophores. It bears both antheridia and archegonia, 

 which resemble the corresponding organs in the eusporangiate 

 Ferns. The antherozoids do not exhaust the protoplasm of the 

 mother cells in which they are developed, but a smaU portion of 

 it remains attached to them on their liberation as in the Ferns. 

 They are biciliate. 



The development of the sporophyte from the zygote is only 

 known in L. Plilegmaria. The first division gives, as before, 

 epibasal and hypobasal segments. The hypobasal cell does not 

 as a rule divide, but elongates slightly to form the suspensor. 

 The epibasal cell gives rise to the embryo, which consists of a 

 primary stem, bearing a single cotyledon. The part of the axis 

 below the cotyledon becomes the pseudo-foot already spoken of. 

 It is really a liypocotyl. There is no primary or true root, but 

 an adventitious one speedil}^ arises from below the cotyledon. 



In two other species {L. cernuum and L. inundatum) the 

 later stages in the development have been followed, but the early 

 ones are unknown. In them the appearance of the primary stem 

 is preceded by the development of a tuberous body which bears 

 the cotj'ledon and subsequently the stem at its apex. From its 

 base adventitious roots arise exogenousl3\ 



Besides these modes of reproduction the vegetative method 

 is not uncommon. Some species of Lj^copodium multiply by 

 gemmae, others b3^ tuberous outgrowths from the roots, others by 

 the detachment of branches. Phylloglossum produces annually 

 a single branch, which^develops into the tuber of the succeeding 

 year. Psilotum sometimes bears gemmae on its rhizomes. 



Section 2.— Heterosporous Lycopodin^. 



In this section we have two genera grouped together, about 

 whose close afhnity there is some doubt. These are Selaginella 

 and Isoetes. Of the relationship of the former to the isosporous 

 Lycopodinae there can be no doubt, but some authorities lean to 

 the view that the affinities of Isoetes are rather to the Ferns than 

 to the present group. This view is based upon its general habit, 

 the large leaves and the small stem being much more like the 



