of Lepidostrobus Brownii , Schpr. 331 
a figure 1 of a rootlet cut transversely near its base, in which 
the outer space is filled with a continuous tissue of thin- 
walled cells ; this is, however, the case only at the extreme 
base ; rather higher up a large cavity is found within the 
peripheral band of cortex, and surrounding the central vas- 
cular strand, and this apparently extends throughout the 
length of the root. At the extreme base the ‘ rootlet cushion,’ 
as Williamson styles the continuous tissue at the base of the 
rootlet, is found to be covered by minute branching tubular 
cells 2 , which project upwards and outwards into the large 
cavity, while some form oblique connecting filaments which 
run to the outer band of cortex. Williamson further remarks 3 
that these cells are * frequently much disorganized,’ while they 
are seen only at the base of attachment of the rootlet to the 
main root. Taking these facts into consideration, together 
with the details of development of the roots of Isoetes , in 
which a somewhat similar space occurs 4 , and also the fact 
that in the internal roots of Lycopodium Selago the outer 
cortex may be found completely separated by an air-space 
of schizogenetic origin from the inner cortex, it will seem 
probable that the outer space in the Stigmarian rootlet was 
chiefly of schizogenetic origin, though filamentous cells such 
as those above quoted appear also to have been present, at 
least in early conditions of the rootlet, and to have under- 
gone disorganization, either during life or prior to complete 
fossilization ; their disorganization would thus contribute 
lysigenetically to the formation of the cavity. 
Turning now to the inner space of the Stigmarian rootlet, 
though this is commonly vacant, it is sometimes found to be 
partially or completely filled with a tissue to which the 
character of phloem is ascribed 5 . It seems probable that in 
the living state this inner cavity did not exist, but that it 
1 loc. cit. PI. IX, Fig. 51. 
2 loc. cit. PI. X, Figs. 43 and 50. 
3 loc. cit. p. 27. 
* See Naegeli and Leitgeb., Beitr. zur wiss. Bot., Heft IV, p. 132, and PI. XIX. 
5 See Williamson, loc. cit. p. 32, PI. XI, Fig. 62. 
