292 
Delf — Studies of Protoplasmic Permeability by 
B. Dandelion Scapes. 
Pith Cavity 
Endodermis 
Epidermis 
Fig. 6. Diagrammatic representation of transverse 
section of middle region of dandelion scape at flowering 
period, x 10. 
It was found that a dandelion scape finishes its most active growth 
in length just before the opening of the inflorescence. In the cases observed, 
the flowers remained open for two days, and during this time there is slight 
growth in length confined 
to the uppermost tapering 
part of the scape. After 
flowering, the bracts close 
over the inflorescence, and 
in about a fortnight they 
reopen for the dispersal of 
the fruits. During this fort- 
night there is active growth 
in length in the basal region 
of the scape, and a certain 
amount of increase in dia- 
meter is also attained — by 
tangential stretching rather 
than by meristematic ac- 
tivity. In collecting material, lengths were always 
cut from the basal region of a straight healthy scape, 
bearing un faded flowers. They were transferred to 
a beaker of water on the spot, and were supported 
vertically to avoid geotropic effects during the in- 
terval between collecting the material and making 
an experiment. 
The scape has a very simple structure and, 
excepting for the epidermis and the l ing of vascular 
bundles, is entirely made up of parenchymatous 
cells, with numerous intercellular spaces between 
them. The epidermal cells are thinly cuticularized. 
Two or sometimes three layers of hypodermal 
cells are narrow radially, elongated vertically, and 
thickened with cellulose on their tangential walls. 
The remaining cortical cells are thin-walled and 
rather longer than broad ; the pith cells are rect- 
angular with square ends and at least twice as long 
as broad. The pith cavity is clearly formed by 
the rupture of the central cells at an early stage, 
and the remains of their torn walls adhere to the 
inner living pith cells. The outer cortical cells 
contain numerous scattered chloroplasts, but starch 
Fig. 7. Parc of trans- 
verse section of middle region 
of dandelion scape taken be- 
tween the larger bundles ; 
drawn with Zeiss D. D. and 
5*5 abjective (Beck). 
