OF LOWER GBEENSAND PLANTS. 21 



represent the xylem-parenchyma. The phloem, endo- 

 dermis, and other soft tissues which must have sur- 

 rounded the stele are not preserved, but are represented 

 bv an outlining configuration of the minute blackened 

 granules in the matrix. " Greensand ; " Potton. 



V. 13081. A fragment, 26 cm. x 14 cm., and evidently half of 

 one of the large lenticular specimens described by 

 Mantell and others as common, which has been split 

 longitudinally. The outer surface, which is convex, 

 is somewhat weathered and rolled, and has fragments 

 of a coarse granular matrix adhering to it ; the inner 

 surface shows the irregular reticulations formed by 

 the weft of rootlets, which often have the appearance 

 of small hollow tubes. The larger axes of the stems 

 ore not conspicuous. The 'specimen is largely silici- 

 fied, and would show an imperfect petrifaction of the 

 tissues in sectiou. Phosphate bed, Potton. 



No history. 



V. 10262. Transverse section of a very poorly petrified frag- 

 ment (2-5 x 2 cm.) showing only rootlets. In several 

 of these the diarch stele can be clearly seen, but the 

 other tissues are almost unrecognisable. Greensand ; 

 Ireland. -A T history. 



Group SPERMOPHYTA. 



Plants in which the alternation of generations is marked by 

 the reduction of the gametophyte and its enclosure within the 

 organs of the sporophyte. " The plant," as we know it, con- 

 sists of the sporophyte, which is differentiated into root, stem, 

 leaves, and sporangia. The " spores " are specialised and 

 develop within protective envelopes, which compounded to- 

 gether form the " seed," and within the seed the much reduced 

 garaetophyte gives rise to an egg-cell which, when fertilised, 

 produces a multicellular embryo which also develops within the 

 the seed. 



Vegetatively the plants vary from delicate filmy water-plants, 

 iri which a secondary reduction of the specialised tissue? can 



