﻿2 20 RELATIONSHIPS. 



considerable distance below an ovule, the outer of the horizontally aligned bundles 

 assumes first a horseshoe (selenic) and then a concentric form as it bends out- 

 ward toward the ovule base, thus presenting at this point a certain similarity 

 to the more compactly organized concentric bundle of the cycadeoideau seed 

 pedicel. On entering the ovule this initial concentric bundle divides into two, 

 three, and finally four or more branches aligned in circular order. Then one of 

 these bundles swings into the center to form the main ovule supply, the remaining 

 peripheral bundles again assuming a circular order. As the central bundle swings 

 in from the peripheral position it resumes the typical mesareh concentric structure 

 before splitting up in the inner flesh under the base of the ovule. Of the peripheral 

 series the two bundles which lie in the common plane of the sporophyll and seed 

 form the branches which traverse the outer and inner flesh, while the two in the 

 vertical plane, although at first greatly enlarged, show a lesser differentiation, 

 and do not pass beyond the base of the seed. The manner in which variations of 

 the bilateral symmetry just described occur within the genus Cycas is made fairly 

 evident by the subjoined diagrammatic figures showing the branching in C. cin iu- 

 alis, C. revoluta, and C. Riuminiana. 



(5) It is a striking fact that in broad contradistinction to the free bilater- 

 ally symmetric seeds of Cycas those of all the other existing genera as borne in 

 compacted cones retain a more or less pronounced radial symmetry. That this 

 radio-symmetry may be ancient and not merely a secondary result of sporophyll 

 appression in compacted cones, as might be suspected from its still more pro- 

 nounced development in the cycadeoideau seed pedicels, is shown by the paleozoic 

 cycadaceous seed Lagenostoma, which is both radio-symmetric and free-borne. 



In the radio-symmetric series several types of bundle arrangement are evident, 

 with many intervening gradations and modifications in different genera and species. 

 In Zamia, one of the most reduced forms, a single bundle runs out from the lamina 

 of the sporophyll and divides beneath the seed base into a minor branch passing 

 on to the outer angle of the peltate end of the sporophyll, and a major crescentic 

 collateral or concentric branch forming the entire seed supply, which subsequently 

 divides into circularly aligned bundles, and then into the two circular series sup- 

 plying the inner and outer flesh by simple branching. (See fig. 128.) 



It is perfectly clear that the final reduction stage of a radially arranged bundle 

 supply originating as a single concentric strand, as in Zamia, must be a single 

 bundle supplying a pedicellate seed analogous to that of the cycadeoideau seed. A 

 distinctly more complex arrangement than that of Zamia is to be seen in one of 

 its least complicated forms in Bowenia spcctabilis. Here two bundles branch 

 off to the sporangium, one after the other, the second, however, sending on a con- 

 tinuation into the outer angle of the sporophyll end. Then, either just beneath 

 the seed attachment or in the seed base, the two basal bundles subdivide into eiglit 

 outer and a greater number of inner flesh bundles. 



In Macrozamia and Encephalarlos the radio-symmetric arrangement is 

 Bowenia-like, but greatly complicated by branching into the outer angle of the 

 sporophyll and in the seed base, no doubt in large part as a physiologic result of 

 the enormous increase in the size of the seed. The least differentiation of seed- 



