﻿DESCRIPTION OF PLATES. 



273 



Plate XXX. Cycadeoidea Wielandi. Transverse Section through Young 

 Seeds, showing a pre-embryonal stage. T. 393. S. 394. X 35- 



See photograph of portion of this section, which cuts transversely through the entire 

 strobilus given in reduced scale, plate xxv, No. 5. At p are the seeds here shown. The 

 section traverses two exterior bracts and the mass of seed pedicels and interseminal scales, 

 inclosing two peripheral seeds in a pre-embryonic stage of growth that may represent the 



proembryo rather than prothallial 

 tissue. The structures present must 

 nearly if not entirely fill the seed 

 cavity, as indicated by the subjoined 

 figures of seeds from sections of 

 several other strobili of T. 393, in 

 a similar stage of growth. 



[With the cutting of further sec- 

 tions there will in the course of time 

 accumulate a series of fully pre- 

 served examples in longitudinal as 

 well as transverse section — in some 

 cases no doubt showing both younger 

 and later stages of growth. Should 

 it be required, a single seed may be 

 studied in serial section by photo- 

 graphing either a tangential, or 

 basal, or an apical polished surface 

 as an opaque object and then re- 

 peatedly polishing and photograph- 

 ing at equidistant levels. These may 

 of course be at any desired distance 

 apart, and the results obtained 

 therefore of absolute completeness. 

 No other process than this, which 

 would destroy the original specimen 

 and leave in its place a series of 

 photographs, would be available for 

 these object-;. To simply let the 

 sections made in the ordinary way 

 accumulate must in the end prove 

 the more wasteful method, since a 

 single one of these small seeds will 

 seldom be traversed by more than 

 two well-placed successively parallel 

 sections. Time for this work has not 

 yet been available.] 



D 



■ jf -Ml 



. ■ mm 



A, from S. 218. X 17. Longitudinal to oblique section cutting dp of 

 seed; B. from same section as the pteceding, showing lower three- 

 fourths of seed fupper portion was not preserved); C and D, approx- 

 imately median oblique sections. 17. The comparison of the 

 various sections illustrated suggests that the large-celled tissue was not 

 so compact throughout all the interior of the seed cavity as at the 

 level of the two transversely cut seed sections shown in the plate. 

 But no such large cavity appears as in the proembryo of Cycas. 



Plate XXXI. Various Strobilar and Foliar Structures of Cycadeoidea?. 



Photomicrograph I. — Cycadeoidea Wielandi (T. 131). S. 34. X 10. Transverse sec- 

 tion through peduncle cut near insertion on cortex and showing a portion of the woody 

 cylinder giving origin to large crescentic bract traces. The strong development of the 

 bundles suggests that the bracts are reduced forms that once fulfilled some higher function 

 than that of mere enveloping organs. 



Photomicrograph 2.— C. turrita (T. 364). S. 113. X 25. Longitudinal section through 

 base of ovulate strobilus (0), showing loose annulus or collar of wilted tissue (s), and a 

 bract base (t) ; v is the peduncle bundle, and it is seen to give off a branch to the left, 

 which, after passing out through the ground tissue with scalariform markings like that of 



