Ancient Plants

[...]preserved outside the castings; and it was then known that the plant had a hollow pith, with transverse bands of tissue across it at intervals which caused the curious constrictions in the cast. Fig. 5.-Leaf Impressions of "Fern" Sphenopteris on Shale. (Photo.) Another form of cast which is common in some rocks is that of seeds. As a rule these casts are not connected with any actually preserved tissue, but they show the external form, or the form of the stony part of the seed. Well-known seeds of this type are those of Trigonocarpon, which has three characteristic ridges down the stone. Sometimes in the fine sandstone in which they occur embedded, the internal cast lies embedded in the[...].