494 Agnes Arber. — On the Structure of the Androecium in 
For the sake of completeness, however, we will now briefly indicate how 
the vascular bundles for the gynaeceum arise. It will be simplest, in the 
first place, to describe an individual case, since there is some variation in 
detail. At about the level represented in Text-fig. I, B, or a little higher, 
two or three branches arose on the inner side of the vascular star, and, by 
their fusion, supplied the ovary with a small central group of vascular tissue. 
This group eventually branched, and the branches distributed themselves 
among the four placentas, where they formed lateral bundles. Then, at 
about the level of Text-fig. i, C, or a little higher, the four bundles, which 
enter the septa and eventually form the main placental bundles, were given 
off internally from four of the five stamen bundles, while the fifth stamen 
bundle and three of the staminode bundles produced, as internal branches, 
the four strands which occupy a median position outside each loculus. In 
a second flower, on the other hand, these four bundles were all produced 
from staminode bundles, instead of one being derived from a stamen strand. 
In the third example, one of these loculus bundles was derived from a stamen 
bundle, two from staminode bundles, while the fourth arose between a stamen 
and a staminode strand before they had separated from the central vascular 
star. In this flower, also, one of the main placental bundles arose from 
a staminode strand, though the remaining three were connected, as in other 
cases, with stamen strands. 
There is thus considerably more irregularity in the origin of the vascular 
supply of the gynaeceum than in that of the other whorls. This is probably 
connected with the fact that there are only four carpels, and, consequently, 
the bundles which supply them cannot be symmetrically related to those of 
the remaining whorls of the flower, which are all pentamerous. 
(ii) The Anatomy of the Stamens in PARNASSIA PALUSTRIS, Z., and 
other Species. 
Even before the stamen bundles leave the axis they show a highly 
anomalous structure. Their xylem, instead of consisting of a single group 
of elements, takes the form, as seen in transverse section, of a more or less 
completely closed ring. I have detected this anomaly, in more than one 
case, immediately after the stamen bundle had given off its branch to the 
gynaeceum : in other words, this peculiarity arises at the very level at which 
the stamen bundle becomes a completely independent unit. The exact 
details of the structure of the strand cannot be made out while it is still in 
the receptacle, owing to the oblique course which it follows, but when it 
enters the filament it can be studied with ease. 
As shown in PI. XXXVI, Fig. i, the xylem is ring-like in section and 
encloses a patch of thin-walled parenchymatous tissue. Small elements, 
which have the characteristic appearance of protoxylem, are attached 
internally to the dorsal side of the ring. That they are, in fact, protoxylem 
