﻿i5o 



REPRODUCTIVE STRUCTURES. 



sterile. Since, therefore, these "disks" have been found as isolated structureless 

 fossil casts or as imprints in so many different countries, an exact knowledge of 

 their form and anatomy is not only of biologic importance, but enables us greatly to 

 extend our knowledge of the distribution of the Cycadeoidege. In the examples on 

 which we in the first instance base the present description, that is, on the flowers of 

 Yale cycad 214, and the Iowa specimen, the central cones of which have just been 

 described, the disk is still more or less strongly attached to the receptacular shoulder, 

 just at the base of the cone, and is as yet unexpanded, although nearly mature and 

 plainly approaching the time of expansion and dehiscence. 



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Fig. 75. — Cycadeoidea dacotensis. Fruit I. Sections 481-484. T. 214. X I3. Four successive transverse sec- 

 tions of a pollen-bearing bisporangiate strobilus cut from trunk in form of cylindrical core. 



a. S. 481. This section cuts through the bract-enveloped staminate disk and the irclcscd ovulalecone. At the center of the cone 



are traces of its bundle cylinder, and exteriorly the outer palisaded zone of interseminal scales and short seed stems about a milli- 

 meter in length. Between the cone and staminate disk a few of the decurvcd tips of staminate fronds are cut. The bundle sys- 

 tem of the staminate disk is shown by the white dots in black ground colcr. The bracts are shown in solid black, and the only 

 one of the surrounding leaf bases cut by the section in stippled surface, with its bundles as dots. 



b. S. 482. Cut two centimeters (proximally) beneath the preceding section. In this section, which passes just beneath the inser- 



tion of the hypogynous staminate disk, nearly all the bracts appear, as well as two of the surrounding leaf bases. 



If reference now be made to figures 72-75, showing serially cut longitudinal 

 and transverse sections, the general features of the non-expanded or preflorate disk 

 will be apparent. In the longitudinal section a heavy petiolar and rachial axis 

 (r, figure 72) rises from the base of the ovulate cone (c) to some distance beyond 

 its summit, and then curves inward and is once deflexed, so that the downwardly 

 turned apical third of its length, which is at first narrow and then widens into a 

 broad spatulate tip, rests on the surface of the central cone. Although the middle 

 region of the rachis, that is, the part curving inward and then downward at the 

 summit of the strobilus, is often eroded away, as the result of its being the highest 

 and most exposed portion, the relations just described would clearly be seen to be 

 the true ones, even if we did not know the intact disk of C. ingens type shown 



