304 GYMNOSPERMOTJS SEEDS [CH. 



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 Aetheo- 

 testa, the thick endotesta of Pachy testa (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, 1) 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. 



The bionomics of Palaeozoic plants is a subject worthy of 

 more serious attention than it has so far received. The search 

 for morphological characters that may have facilitated the 

 wanderings of widely distributed genera and species and a closer 

 investigation of physiological-anatomical problems presented by 

 the vegetative organs of petrified plants would not only extend 

 our knowledge of the morphology of ancient types but would 

 stimulate comparative study and, incidentally, relieve the dullness 

 of pure description. It may be argued that we should first 

 establish a more solid foundation by further observations on 



