. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. [• IG. 145- A = the sporophylls no longer serve as assimilating leaves, but appear as chaffy scales, performing a protective function. It would be difficult to read from the comparative study of the mature sporophyte in the genus Lycopodium any other evolutionary story than this. The only other living genus of eligulate Lycopods is the monotypic Phylloglossum, long recognised as the simplest of them all. The mature plant as seen above ground consists of a tuft of almost cylindrical assimilating leaves
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. [• IG. 145- A = the sporophylls no longer serve as assimilating leaves, but appear as chaffy scales, performing a protective function. It would be difficult to read from the comparative study of the mature sporophyte in the genus Lycopodium any other evolutionary story than this. The only other living genus of eligulate Lycopods is the monotypic Phylloglossum, long recognised as the simplest of them all. The mature plant as seen above ground consists of a tuft of almost cylindrical assimilating leaves, from the midst of which rises the simple axis terminated by the short strobilus ; below ground are found two ovate storage tubers, one dating from the preceding year and in course of exhaustion, the other in course of development as a store for the succeed- ing year. There are also one or more roots (Fig. 145). The lower parts of this curious little plant cannot be properly understood till it is compared with the embryos of certain species of Lycopodium, for it repeats in its annual growths their embryonic characters : the discussion of them will therefore be postponed (p. 351). The very short strobilus shows a similarity to the Urostachya rather than to the Rhopalostachya section of the genus : this is seen in the smooth margin of the rather fleshy sporophylls, as well as in the incomplete protection of the sporangia. It is interesting to note that tran- sitions are occasionally found between the foliage leaves (protophylls) and the sporophylls : Fig. 146 a shows a case where a single sporophyll of larger size than the normal, with a sporangium in its axil, stands isolated some way below the strobilus : thus it is intermediate both in position and in character between the two types. A small protophyll without any sporangium may also sometimes be found at the base of the pedicel. Dichotomous branching of the strobilus is some- times seen, but it is rare : an example is show
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