538 Bancroft.—A Contribution to our 
a stage in the production of the outer cortex just above branch separation. 
The large-celled epidermis is still distinct at this point; no traces of stomata 
have been observed. 
iii. /3 type .—The stems of R. cylindrica described and figured by Hick 
are, with one exception, referable to this type 1 ; the occurrence of the two 
forms is not specially mentioned by this author. 2 
Stems of /3 type are similar in size to those of a type, but are dis¬ 
tinguished from them by the relatively small size of the cylindrical xylem 
strand, of which the average diameter is 0-4 mm. This strand typically 
possesses a single central protoxylem group, so that a condition of true 
endarchy is realized (PI. XXVI, Figs. 3 and 7). The occurrence of more than 
one protoxylem in this case seems normally to be in connexion with branch- 
Text-fig. 4. a , Separation surface of an a petiole, showing the epidermis ( ep. ). Note the 
absence of the narrow, thin-walled cells underlying the epidermis (cf. Fig. 3). b, separation surface 
of an a stem, showing the irregular epidermis, and an epidermal hair ( h .). The narrow, thin-walled 
cells are absent here also, c, a portion of an oblique longitudinal section of an a stem, showing two 
hairs of which the connexion with the epidermis cannot be observed, x 80. ( a, and b , from slide 
K 20 m ; c , from slide K 21 h, University College, London.) 
mg (Text-fig. 8); and apart from the narrow elements of the protoxylem 
group, there is no differentiation in size between central and outer tracheides. 
The elements are all of the type of the outer tracheides in a stems, although 
they are less in diameter (70 /x) (cf. PI. XXVI, Figs. 1 and 8). 
The three cortical areas are again distinguishable in /3 type stems. 3 
The inner cortex is composed of two or three series of tangentially 
elongated cells (PI. XXVI, Figs. 3, 8, and 9), the walls of which are firm but 
not thickened to any extent. There is a varying tendency towards concentric 
arrangement of the inner cell-series, and the gradual transition to the middle 
cortex takes place as in a stems. 
The middle cortex consists of rounded or polygonal cells, thin-walled, 
and somewhat irregular in size. Near the inner limit of this area is a band 
1 Hick (’ 96 ) : the exception is figured in PL I, Fig. 5. 
2 Williamson figures and notes the two forms of stem ; his Fig. 88 is a P type stem. 
3 Cf. Hick’s description (’ 96 ), p. 4. 
