﻿2 26 RELATIONSHIPS. 



mesarch cylinder and approximately concentric and fern-like rather than collateral 

 cortical traces. The same must perforce be true of the Cycadeoideae. 



Fruits. — After fertilization the cones do not greatly increase in size, and finally 

 fall apart, except in Cyras, where the carpellary leaves in the course of ripening 

 bend in and out amongst each other and are at last shed, less their bases, like the 

 foliage leaves, a series of which then follows with continued growth of the axis. 

 The mature seeds of the compacted cones do not reach such great size as those 

 borne by the free carpels of Cvcas, which in some species are as large as goose eggs. 

 All have heavy woody walls, but as the main structural features of the seed coats 

 have already been treated, aud as the extensive subject of related Paleozoic seeds can 

 not be here taken up, it only remains to consider the embryos and their formation. 



After the semi-aquatic zoidogamic fertilization already mentioned, the oospore 

 as embedded in the large endosperm enlarges, and free nuclei appear in the cyto- 

 plasm, as first determined by Treub (\G-jb). Further details concerning the man- 

 ner in which the initial nuclear division takes place have been given by Ikeno (69), 

 but are omitted. Free nuclei now become very abundant, and then, following 

 the vacuolation and disorganization of the central region, all of the cytoplasm is 

 massed at the base of the spore and parietally, with a single or in places double 

 parietal layer of equidistautly embedded nuclei, except at the base, where there is 

 some nuclear massing. This is the young proembryo, which, after further nuclear 

 division and the appearance of cell walls, encroaches on the central cavity, but 

 never fills it up with tissue, as in the "protocorm" of Ginkgo. It is this sac-like 

 proembryo of Treub, or preembryonal structure, embedded in the endosperm, 

 immediately preceding suspensor development, which we may in the first instance 

 hope to find differentiated in silicified seeds, though it is not impossible that yet 

 earlier purely nuclear arrangements may also be found indicated. Suspensor 

 development next intervenes. Cells of the basal mass adjacent to the terminal cell 

 develop, by division and elongation, a remarkably long, tortuous, unbrauched and 

 massive suspensor, which emerges from the lower archegonial region in a fascicle, 

 with disorganization of adjacent tissue. It is the suspensor tips which bear the 

 cells that initiate the formation of the embryo, the early stages of which have been 

 as yet but little studied. But a single embryo is formed from one archegonium, 

 though according to the number of archegonia present several may be developed 

 to the seed. The embryos are small and deeply embedded in endosperm, and the 

 number of cotyledons is stated to be one in Ceratozamia, two in Cyras and Zamia, 

 and one to three in Macrozamia spiralis. 



SUMMARY OF RELATIONSHIPS OF CYCADEOIDEAN TO EXISTING CYCADS. 



In the foregoing sketch of the existing cycads reference has been quite con- 

 stantly made to details offering distinct structural agreements with or variations 

 from the fossil forms. It is therefore next in order to summarize in a much more 

 compacted view and more general terms those features of primary physiologic and 

 morphologic significance in determining the phyletic and taxonomic values of the 

 two groups, as well as that position in current classifications which best expresses 

 the known facts. 



