770 
Notes. 
of Coniferae, a relic of an ancient, ancestral character. But I am 
still quite willing to admit that this view of the tissue concerned may 
be an erroneous one. The quasi centripetal xylem of the inverted 
strands permeates the cortex in the same way as does that of the 
central cylinder the pith. 
But there is another interesting point exhibited by the primitive 
floral axis of Welwitschia . I recognize an ancestral type of structure 
in the presence of the concentric, or partially-concentric, strands 
outside the central cylinder. These strands are, however, as must 
necessarily follow from the fact that they eventually supply lateral 
axes, primary in origin ; but I nevertheless regard them as homologous 
and comparable with the strands composing the second cylinder in 
the vegetative axes of four genera of Cycads and of Welwitschia itself, 
which are not primary but secondary in origin. 
I do not myself consider it necessary, as regards the phylum of 
plants with which we are dealing, but, on the contrary, rather mislead- 
ing, to lay much stress on the difference between primary and secondary 
structures ; for the various cylinders, where they occur, all have, with 
the exception of the insignificant and often transitory protoxylem and 
protophloem of the former, exactly the same constitution and appear- 
ance. In fact, it seems to me that the only difference between them, 
and that an unimportant one, lies in the varying periods at which they 
are formed. All the cylinders, from the innermost primary one 
outward, must be homologous one with another. The phenomenon 
here exhibited by Welwitschia I believe, however, to be parallel with 
the case of Medullosa Leuckarti , Gopp. and Stenz. 1 , in whose stem two 
primary cylinders have been described; with that of Ceratozamia 
mexicana, Brongn., and C. latifolia , Miq. 2 3 , in the axes of whose male 
cones I have myself described what I believe to be the rudiment of an 
intrafascicular primary cylinder of bundles ; and, finally, with that of 
Encephalartos 8 , the male and female cones of which exhibit in their 
axes two cylinders of primary bundles, the outermost of which sup- 
plies the sporophylls, and, in consequence, dwindles in the extent 
of its development towards the apex of the cone ; in both Welwitschia 
1 Weber und Sterzel, ‘ Beitrage zur Kenntniss der Medulloseae,’ p. 42, and 
Plate IV, Fig. 2, 1896. 
2 Worsdell, ‘ Contributions to the Comparative Anatomy of the Cycadaceae,’ 
Trans. Linn. Soc., vol. vi, pt. 2, p. uy, and Plate XVI, Figs. 10 and 11, 1901. 
3 Ibid., p. 1 16, and Plate XV, Figs. 7 and 9. 
