OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
11 
met with in the coal-fields of Lancashire*. Some of them I have obtained myself. For 
others I am indebted to Mr. Lutterworth ; but for my best examples I had to thank 
the late Mr. J. Whittaker f. 
With two exceptions my specimens are confined to small masses of the adventitious 
roots so characteristic of the Psaronites and arborescent Ferns; but in two instances I 
have obtained the outer layer of epidermal and subepidermal tissue from which the 
rootlets more immediately sprang. Fig. 18 represents a transverse section of one of 
these of the natural size ; the outer or cortical parenchyma of another specimen with 
several rootlets passing downwards and outwards through it is enlarged 24 diameters in 
fig. 19. This cortical layer consists of a somewhat irregular parenchyma, composed of 
cells which are usually from about -01 to ‘006 in diameter. At the innermost portion 
of this cortex (fig. 19, b) the structure is somewhat confused; the regular parenchyma 
has interspersed through it a number of irregular cavities, each of which seems to have 
been either a large cell, or to have resulted from the rupture of two or three cells which 
have united to form a common cavity. As we proceed outwards, the cells ( b ') become 
somewhat larger than at the inner portion of the cortex. At i, i we have several 
rootlets seen in transverse section, some of them being divided into two halves by an 
accidental fissure which has extended through this portion of the bark and been filled 
up with infiltrated crystalline carbonate of lime. At b" we find the parenchymatous 
cortical cells increasing still further in size, becoming lax in their aggregation, and 
finally being prolonged into a number of epidermal hairs such as frequently clothe the 
adventitious roots of living tree ferns — such, for example, as Cyatliea dealbata. 
Fig. 20 represents an enlarged portion of fig. 18, which latter is a cluster of adven- 
titious rootlets free from the cortical parenchyma which encloses them in the case of 
fig. 19. Here the interspaces between the rootlets are seen to be occupied by numerous 
epidermal hairs. Fig. 21 is a portion of fig. 19 yet more highly magnified. 
Each rootlet, when free from the cortical parenchyma, has a diameter of from -075 toT2. 
Externally it consists of a very well-defined cylinder of sclerenchymatous prosenchyma 
(figs. 20 & 21, 1). This cylinder-wall is from -012 to -015 in thickness. The fibres of 
which it is composed have a diameter of from -00125 to -003. Within this cylinder 
there has doubtless been a mass of cellular tissue, which has disappeared in every instance 
that I have yet seen ; but each rootlet retains more or less distinct traces of the central 
bundle of small vessels (fig. 20, m ). Their state of mineralization prevents my deter- 
mining their characters with absolute certainty ; but some of the fragments indicate that 
* Since this Memoir was read I find that fragments of tree ferns with aerial roots were figured and described 
hy the Rev. Henry H. Higgins, M.A., “ On some Fossil Ferns in the Ravenhead Collection, Free Public 
Museum, Liverpool,” p. 3, pi. 11. figs. 2 & 3, — June 2nd, 1876. 
t I much regret that since my last memoir was read I have to speak of this valuable auxiliary in the past 
tense. He was an excellent example of the scientific operative for which Lancashire has so long been cele- 
brated. His zeal for the investigation of the plants of the Coal-measures was only equalled hy the open- 
handed liberality with which he placed his valued treasures at the disposal of any one who was able and willing 
to use them for scientific purposes. 
C 2 
