66G 
PROFESSOR F. 0. BOWER ON THE DEVELOPMENT AND 
authors on Phylloglossum. This memoir will therefore deal merely with the observa¬ 
tions recently made by the author ; in some points it will be seen that they confirm 
the observations of previous writers, in others they are not in accord with them : 
they will be placed in relation with those of other authors w T hen the investigations, 
which are still in progress, have been as far as possible completed. 
Structure of the Tuber during the resting stage. 
The tubers as sent over from South Australia were in the mature condition, and 
undergoing a period of rest. The upper parts of the plants which produced them had 
already died off. In no case was there evidence of more than one tuber being- 
produced by one parent plant. 
In this condition the structure of the tuber is as follows : it consists of an ovoid 
solid mass of tissue, connected at its upper end with the stalk by which it was 
attached to the parent plant. This stalk widens out near the apical end of the tuber 
(i.e., that nearer the parent plant), and is there hollowed, covering in the broad 
organic apex of the tuber, which thus has the appearance of being of endogenous 
origin. A transverse section of the stalk which bears the tuber shows a nearly 
circular outline. The chief bulk of the tissue consists of thin walled parenchyma, 
with intercellular spaces : in this may be recognised a point where the cells are of 
smaller size, and for the most part without intercellular spaces (fig. 1, c) : in many 
cases a transverse section will show a cavity between these cells (c, fig. 2), and this is 
especially marked in sections taken near the tuber, or near the attachment of the 
stalk to the parent plant. At the point in question lies the original channel of com¬ 
munication of the apex of the tuber with the outer air; as will shortly be seen the 
apex of the tuber is of exogenous origin, but the channel of communication becomes 
closed during development. Further, a vascular strand of small size may be seen cut 
through in the transverse section (xy, fig. 1); it consists of a few elements with 
lignified walls, which are, as shown by longitudinal sections, spirally or reticulately 
thickened. At the periphery is a layer of epidermis, with peculiarly thickened walls: 
it is continuous with a similarly developed layer covering the tuber externally (see 
below). Passing downwards to the tuber itself, the stalk widens out, and becomes 
hollowed; the vascular strand spreads laterally, so as to assume a funnel-like form, 
covering the apex of the tuber; but it stops short about the level of the apical cone, 
and is not continuous into the fleshy tissue of the tuber. 
The mature tuber itself consists of a central bulky mass of thin walled parenchyma, 
which is entirely undifferentiated : there are intercellular spaces. The cells are filled 
with store materials, viz,, protoplasm, starch and oil. Towards the periphery of the 
tuber the cells have little or no contents, and the last two or three layers below the 
epidermis thus form a more transparent band, the elements being often squeezed out 
of shape. The superficial layer is developed as a clearly defined epidermis (figs. 3, 4); 
the cells themselves are of oblong form, their radial walls are strongly thickened and 
