The leafy nature of the seed-bearing scale is an important and interesting feature. Although theoretically botanists are accustomed to accept the view that seeds are always borne on specially modified leaves (so that to a botanist even the “shell” of a pea-pod and the box of a poppy capsule are leaves), yet in _Cycas_ alone among living plants are seeds really found growing on a large structure which has the appearance of a leaf. Hence, from this point of view (see p. 45, however, for a caution against concluding that the whole plant is similarly lowly organized), _Cycas_ is the most primitive of all the living plants that bear seeds, and hence presumably the likest to the fossil ancestors of the seed-bearing types. In this character it is more primitive than the fossil group of the _Cordaiteæ_, and comes very close to an intermediate group of fossils to be considered in the next chapter. [Illustration: Fig. 76.—Seed of _Cycas_ cut open _n_, The nucellus, fused at the level _l_ to the coat _c_; _sc_, stony layer of coat; _p.c_, pollen chamber in apex of the nucellus; S, “spore”, filled with endosperm, in which lies the embryo _e_.] To enter into the detailed anatomy of the seeds would lead us too far into the realms of the specialist, but we must notice one or two points about them. Firstly, their very large size, for ripe seeds of _Cycas_ are as large as peaches (and peaches, it is to be noted, are fruits, not seeds), and particularly the large size they attain _before_ they are fertilized and have an embryo. Among the higher plants the young seeds remain very minute until an embryo is secured by the act of fertilization, but in the Cycads the seeds enlarge and lay in a big store of starch in the endosperm before the embryo appears, so that in the cases in which fertilization is prevented large, sterile “seeds” are nevertheless produced. This must be looked on as a want of precision in the mechanism, and as a wasteful arrangement which is undeniably primitive. An even more wasteful arrangement appears to have been common to the “seeds” of the Palæozoic period, for, though many fossil “seeds” are known in detail from the old rocks, not one is known to have any trace of an embryo. A general plan of the _Cycas_ seed is shown in fig. 76, which should be compared with that of _Ginkgo_ (fig. 68). The large size of the endosperm and the thick and complex seed-coats are characteristic features of both these structures. Another point that makes the Cycad seeds of special interest is the fact that the male cells (as in _Ginkgo_) are developed as active, free-swimming sperms, which swim towards the female cell in the space provided for them in the seed (see _p.c_, fig. 76).