251 
The Anatomy of the Mummy Pea. 
other hand, has an inverse orientation of tissues: the xylem lies 
towards the exterior, and cambium, phloem, pericycle and endodermis 
lie successively nearer the geometrical centre of the axis. Moreover, 
within the endodermis are found a few layers of parenchymatous 
cells resembling a cortex, containing chlorophyll and interpenetrated 
by air spaces ; and these are bounded on the inside by a well-defined 
epidermis with cuticle and numerous perfect stomata, this internal 
epidermis surrounding the large central air cavity (Figs. 1, 2, 3). 
Fig. 3. Diagram of a T.S. of the whole axis at the level of “ p.c." in 
Fig. 1. (Xylem black, phloem clear, pericycle fibres shaded). 
In between the two rings of vascular bundles is found a zone 
of parenchymatous tissue, histologically like a medulla; and like the 
pith in the normal stem this tissue becomes fistular when beyond a 
certain age. The result is that the two rings of vascular and other 
tissues become separated in the mature state by a cylindrical 
lacuna bounded by torn medullary cells (Fig. 3). If the stem be 
cut open in the lower part of the dilated region the internal ring of 
tissues can be seen hanging freely within this lysigenous space, or 
attached only at the slender thread-like tip 1 (Fig. 1). The internal 
1 It was the curious appearance of this internal cylinder that 
attracted the attention of Miss E. L. Stephens, to whom I 
am indebted for the suggestion of an anatomical study of the 
structure. The appearance is in some respects like that en¬ 
countered in certain cases where medullary bundles are 
present and where these persist as isolated cords after the 
embedding pith has been ruptured. Mr. Shrubbs of the 
Cambridge Botany School kindly gave me a petiole of 
Hcracleum giganteum shewing one such cord originating in a 
nodal diaphragm, and containing a single collateral vascular 
bundle. This phenomenon is, however, of a different kind 
from that here described in the Mummy Pea. 
