156 
PROFESSOR W. C. WILLIAMSON" ON" THE ORGANISATION" 
dated with two distinct, though not wholly dissimilai', rhizomes. The French savant 
described the two genera Zygopteris and Anachoropteris as distinguished primarily by 
the differences between these petioles, but secondarily by the differences between 
their rhizomes. 
In my memoir, Part VIII. (‘Phil. Trans.,’vol. 167, pp. 217 et seq.), when de¬ 
scribing a new rhizome and its petioles, under the name of Racliiopteris corrugata, 
I gave at some length my reasons for not multiplying generic names for these 
curious plants ; pointing out how wholly impossible it was to classify recent Ferns 
on any such basis, a fact the importance of which is further illustrated by the 
rhizome which I am about to describe. 
Some weeks ago, my young auxiliary collector, Mr. Lomax, to whom I was indebted 
for the Calamitean fruits described in my last memoir, Part XIV., brought me a 
specimen having the central vascular axis of M. Penault’s Anachoropteris Decaisnii, 
with petioles of the true Zygopteroid type : thus demonstrating that the axis found 
by Renault in connection with a petiole of Gouda’s type of Anachoropteris was 
equally tlie axis of a Zygopteroid petiole. The specimen has been a drifted fragment, 
now imbedded in a hard ganister full of Goniatites. 
Fig. 1 (Plate 1) shows the five-rayed transverse section of the vascular axis of the 
stem or rliizome ; at a is a vacant spot, occupied in some sections by a delicate 
parenchyma—obviously a medullary one—five thin prolongations of which, a', a , are 
projected into five rays of the vascular axis h. This axis is composed of a mass of 
scalariforrn tracheids. Eacli centrifugal ray first contracts in diameter, and then 
expands again, terminating in a truncated, more or less bifurcated extremity. The 
maximum diameter of this axis from the tip of one ray to that of another is p’ather 
more than a quarter of an inch. At h' the end of one of these rays is detached, 
apparently to form the vascular centre of a lateral appendage. At c is a thin band 
of structure superficially resembling a bundle-sheath ; a similar investment encom¬ 
passes not only the central axis, but each of the separate organs.! Apparent rootlets 
are seen at cl. 
Fig. 2 is a second transverse section through the vascular axis, h, of a specimen 
like fig. 1, from which it differs oidy in one or two respects. Thus, the detached 
bifurcate end resembling that of the ray h' of fig. I is replaced at fig. 2, h', by a 
cylindrical vascular bundle, ‘05 of an inch in diameter, whilst the corresponding 
one at h" lias disappeared ; between the bundle h' and its investing zone, c, are 
remains of cellular parenchyma. The black masses e, e are the carbonised remains 
of the cortical parencliyma. 
Fig. 3 is part of another section like fig. 2, but in which the circular section of a 
* Log. cit., Plate IV., fig. 4 his, and Plate V., fig. 5. 
t In a recent memoir, to be referred to on a later page. Professor Stenzel, of Breslau, describes 
specimens which show that these bands do represent zones of specialised, more or less sclerous, cortical 
tissue. 
