228 Sargent.—Fragments of the Flozver Biology 
causes clouds of pollen to float lazily away from its dark green heads, if the 
plant is examined first thing on a still morning. 
I have met with one rather remarkable instance of autogamy in the 
case of Levenhookia pusilla, R. Br. The plant is very tiny, often scarcely 
half an inch high. Its pretty pink blossoms are borne in a compact 
terminal panicle. The corolla measures about one millimetre across. The 
galeate labellum (fifth petal) closely embraces the erect gynostemium 
throughout the flower’s lifetime unless disturbed. The anthers are mature 
at anthesis and dehisce within the labellum. A few days afterwards the 
stigmas are forced up between the anthers by growth of the style apex 
and receive pollen in the process. In due course fruit matures. That 
appears to be the usual process. Sometimes, I believe, the labellum is 
forced off the column by an insect. It seems scarcely possible for one to 
dip into the blossom without dislodging the labellum as it leaves. Once 
dislodged the labellum never again embraces the column ; so that a flower 
once visited is dependent upon insect aid for pollination (unless it had 
been self-pollinated before the visit). I believe the process is exactly 
similar in L. stipitata , F. Muell. In both these species the labellum fits 
the column very closely, and is quite devoid of irritability. This is of 
special interest, because in ‘ Flora Australiensis *, vol. iv, p. 34, Bentham 
states that in contrast with the irritable column of Stylidium , the labellum 
is irritable in Levenhookia. I have only seen the two species named 
above. In these loss or lack of irritability has made the labellum an 
excellent organ for autogamy. This has permitted reduction in size of 
flower and plant, and made possible the occupation of the arid situations 
where I have seen it growing. 
Throughout this paper I have arranged my examples in inverse order 
of th z mechanical complexity of their flowers. I have avoided phylogenetic 
considerations, which it seems to me could only have tended to obscurity 
and contention. From the mechanical view-point the flowers of the 
Proteaceae I have mentioned for simplicity and economy of tissue are 
a very close approach to perfection, if not, indeed, perfection itself. Yet it 
is a genus of Myrtaceae— Eucalyptus —that forms the dominant vegetation 
of this country. The perfection of its floral structure is certainly not the 
only factor governing the measure of a plant’s success—often, perhaps, it is 
of little consequence. There are, however, considerations which suggest 
that the Proteaceae have over-specialized flowers, their mechanical perfection 
being a physiological fault, for the simple reason, I suppose, that their 
pollinators fail to behave in a mechanically perfect manner. Recently 
I estimated the number of flowers borne and seeds produced by two trees 
growing within sight of one another. One was a Jarrah (. Eucalyptus margi - 
nata , Sm.) and the other Banksia attenuata , R. Br. In round numbers the 
former bore six hundred and seventy thousand (670,000) flowers and 
