THE FLORA OF THE EARLY MESOZOIC. 



179 



of that country are of small size/ and may have been of 

 low growth, so that they may have been protected by the 

 snows of winter. The cycads have usually simple or un- 

 branching stems, pinnate leaves borne in a crown at top, 

 and fruits which, though somewhat various in structure 

 and arrangement, are all of the simpler form of gymno- 

 spermous type. The stems are exogenous in structure, 

 but with slender wood and thick bark, and barred tissue, 

 or properly as tissue intermediate between this and the 

 disc-bearing fibres of the pines. 



Though the cycads have a considerable range of or- 

 ganisation and of fructification, and though some points 

 in reference to the latter might assign them a higher 

 place, on the whole they seem to occupy a lower position 

 than the conifers or the cordaiteae of the Carboniferous. 

 In the Carboniferous some of the fern-like leaves assigned 

 to the genus Noeggerathia have been shown by Stur and 

 Weiss to have been gymnosperms, probably allied to 

 cycads, of which they may be regarded at least as pre- 

 cursors. Thus the cycadean type does not really consti- 

 tute an advance in grade of organisation in the Mesozoic, 

 any further than that, in the period now in question, it 

 becomes much more developed in number and variety of 

 forms. But the conifers would seem to have had preced- 

 ence of it for a long time in the Palaeozoic, and it replaces 

 in the Mesozoic the Cordaites, which in many respects 

 excelled it in complexity. 



The greater part of the cycads of the Mesozoic age 

 would seem to have had short stems and to have consti- 

 tuted the undergrowth of woods in which conifers at- 

 tained to greater height. An interesting case of this is 

 the celebrated dirt-bed of the quarries of the Isle of Port- 

 land, long ago described by Dean Buckland. In this 

 fossil soil trunks of pines, which must have attained to 

 great height, are interspersed with the short, thick stems 

 of cycads, of the genus named Cycadoidea by Buckland, 



