Among the numerous types of Palaeozoic seeds are several which invite comparison with the fruits or carpels, apart from the seeds, of Angiosperms. Impressions of _Samaropsis_ seeds (figs. 502, B–K; 503; 504) bear a close resemblance to the laterally expanded fruits of the common Crucifer _Thlaspi arvense_; the ribbed testa of _Hexagonocarpus_ (fig. 506, H) and other genera recalls the fruit-wall of _Alstroemeria_; the recently described Lower Carboniferous seed _Thysanotesta sagittula_ Nath. (fig. 506, F) simulates a carpel of _Erodium_. These and similar instances of a close parallelism in external features between organs that are not homologous, though in themselves of no morphological significance, are at least interesting as illustrating the plasticity displayed by reproductive structures, which in the Palaeozoic period marked a morphological achievement comparable in its importance with the still greater achievement represented by the highly specialised fruits of the modern Flowering plants. The range in form and surface-features of Angiospermous fruits was foreshadowed by Palaeozoic seeds. Structural types and in some cases, superadded to these, features which may reasonably be supposed to have facilitated dispersal had been acquired by the seeds of Palaeozoic plants in forms that in a much later period were adopted by fruits even to a greater degree than by seeds. Characters useful in seed-dispersal, that are now shared by fruits and seeds, are illustrated by the fleshy and possibly edible seeds of extinct Gymnosperms, the plumes and hairy beak of _Gnetopsis_ (fig. 494, E) and _Thysanotesta_ (fig. 506, F) suggestive of feathery stigmas and other appendages. The lacunar sarcotesta of _Aetheotesta_, the thick endotesta of _Pachytesta_ (fig. 497), and the air-chamber of _Codonospermum_ (fig. 498), are strictly comparable with aids to buoyancy in fruits of existing Flowering plants. The mucilage-hairs and superficial cells in _Physostoma_ (fig. 494, I) and _Stephanospermum_ may be compared with the thick mucilaginous investment of the megaspores of recent water-ferns and with similar tissues of some Angiospermous seeds.