﻿EXISTING AND FOSSIL CYCADS COMPARED. 



2 19 



fruit, it doubtless will be, since the pollen chamber has been observed to contain 

 pollen in several cordaitalean species and was found "choke full" in one seed of 

 Lyginodendron. Beneath the pollen chamber lie the archegonia, 2 to 10 in num- 

 ber, often 3 to 6, embedded in the large prothallus. The integument of the ripe 

 seed is three-layered^ tlie middle stony stratum being bounded by an outer and inner 

 flesh (162). It is, however, extremely probable that this integument arises from 

 the fusion of two simpler envelopes, the inner being nucellar, more especially since 

 two such are indicated in the Paleozoic cycadaceous seed Lagenostoma. 



.J a -* 



O 



o 



f 



© 



© 







o 



c. 



o 



G 

 O 



© 



Fig. 128. — Diagrammatic serial transverse sections of bilateral (I to 3) and radio-symmetric (4) bundle traces leading 

 from the laminar bundle series of the sporophyll into the seed base, together with longitudinal sections of seeds 

 showing the same (5 and 6). 



I . Cycas circinalis ; 2, C. revoluta ; 3, C. Riuminiana ; 4, Zamia muricata ; 5, Bowenia spectabilis ; 6, Zamia integrifolia. a (in I E) , 

 disappearing bunjle resulting finally in bilateral symmetry; c (in 1 F). central concentric bundle leading into the chalaza : 

 o (in I F), bundle leading to outer flesh, with branch (i) leading to inner flesh (cf. corresponding notation in figure 127); D (in 

 3), condition at seed base; E (in 3), bundle branching in seed base. In figure 6: A, outer flesh; AV, outer main bundle 

 with branch AV; S, stony median layer of seed ; W, inner flesh, presumably the outer envelope of the nucellus ; T, separation 

 zone; B, the single seed supply bundle. (From Marie C. Stopes.) 



Bundle system of the seed. — The seed and pedicel bundle features but recently 

 elaborated by Miss Stopes (162) are, needless to say, of the utmost importance in 

 forming conceptions of relationships with the Cycadeoidea.-. 



(a) In Cycas circinalis six or more mesarch collateral bundles traverse the 

 petiole and rachis of the carpellary leaf in a horizontal plane, the centripetal xylem 

 being preponderant near the carpellary leaf base, and diminishing to half or less 

 than half of the xylem area uear the attachment of the lowermost ovules. A 



