﻿FOLIAGE. IOI 



and it seems that in general appearance the mature expanded frond may have been 

 quite comparable to that of Zamia floridana, with truncate fronds and twenty to 

 thirty pinnules on each side of the rachis. In several of these fronds but a few 

 millimeters across, as cut in folded-up or prefoliate position and figured by the 

 writer (195, plate lxii, fig. 2), the bundle system is already quite well developed, so 

 minute may be the fronds and yet clearly display their main structural characters. 



Rachis. — The fluted character of the rachis as seen in the photograph of the 

 transverse section (plate xviii) is probably not constant, since the young frond cut 

 on the same level about a centimeter distant shows a nearly round section, of much 

 the same size and form as the young fronds of Zamia floridana. In this younger 

 frond of Cycadella the bundle system is but little developed, the well-preserved 

 tissues showing that they are young, well stored with nutritive material, and 

 ready for rapid elongation and bundle development. In the larger of the fronds, 

 however, the rachial bundle system is clearly indicated by the well-preserved xylem, 

 and the bundles dispose themselves in the form of a closed outline of a heavy V> 

 as was suspected in the fairly well grown rachis of Cycadeoidea, and as partly 

 indicated by the course of change in the leaf-base bundle pattern. 



Histology. — Owing to the small size of the fronds, there is some difficulty in 

 securing exactly transverse sections of the rachis and pinnules ; yet this must be 

 done if the very best results are to be secured. In the sections cut, however, there 

 is a close approach to the ideal result which will answer all the requirements for 

 description of the main structural features, bearing in mind that at best in such 

 young growths as these it can scarcely be expected that all of the tissue zones 

 would, as the result of any natural iron staining, show cell structure equally well 

 throughout, although the differentiation of structure is on the whole surprisingly 

 satisfactory. The upper surface of the frond is formed by a heavy cuticle. The 

 epidermal cells are large and distinct and overlie a more or less continuous layer 

 of hypodermal sclerenchyma a single cell in thickness. The parenchyma beneath 

 may have developed a palisaded layer during subsequent growth, but preservation 

 is indistinct. In any case the parenchyma is not interrupted by the sclerenchy- 

 matous extension of the bundle sheath seen in Cycadeoidea. The free bundles are 

 all distinctly enveloped by a well-conserved cylindrical bundle sheath several cells 

 in thickness, nearly as in Cycadeoidea. The xylem is well preserved, with small 

 protoxylem cells at the center of the xylem area, indicating typical mesarch structure 

 without radial arrangement of the centrifugal wood. No phloem is preserved. The 

 spongy parenchyma is indicated beneath the bundles by a narrow, deeply stained 

 band. The nether portion of the pinnules is made up of one to two layers of 

 sclerenchyma cells, with slight traces of thickening between the bundles. In size 

 and development of all their tissue regions the pinnules of Cycadella are very near 

 to those of the existing cycad Boivenia spcctabilis, as shown in figure 50. 



From the preceding description it will be noted, first, that while the leaf 

 structures of Cycadella present certain differences from those observed in Cyca- 

 deoidea^ there is a general agreement, just such as one might expect to find in two 

 closely related genera of living cycads. Secondly, the structure of the pinnules of 

 Cycadella is found to be almost identical in general disposition and development of 



