wut] THE MECHANISMS OF FLOWERS. 255 
by humble-bees, are sulphur-yellow, and only remain purple at the 
base. I say only remain purple at the base, because this colouring 
is now useless, and seems only explicable as a remnant inherited 
from purple-flowered ancestors. The sulphur-yellow colour of 
empervivum Wulfenii seems not to stand on the same rank as the 
yellow colour of some Sedums; but rather to have been developed 
from a purple colour by the selective influence of humble-bees. 
In connection with the size of the flower, we see in many 
Crassulaceze the number of the parts increased or decreased : 
increased in Sedum from 5 to 7, in Sempervivum arachnoideum 
to 9—11, in S. montanum to 9—12, in 8. Funkii to 10—13, in S. 
ectorum to 11—13, in S. Wulfenii to 13—16; decreased in 
x Re iliarda, DC., to 4, in Tillwa, L., to 3 (609). 
Orv. DROSERACEZ. 
Drosera, L., occurs with cleistogamic flowers (169). 
Orv. HALORAGE. 
——s- Callitriche verna, L.—The proterogynous flowers are figured by 
Axell (17). Axell considers them to be anemophilous; Ludwig 
le ooks upon the submerged flowers as hydrophilous, and the others 
as entomophilous (435). 
— Myriophyllwm spicatum is anemophilous, and I. verticillatum is 
partly anemophilous and partly hydrophilous, according to Ludwig 
(435). 
Orv. COMBRETACE &. 
— Combretum, L., is very diligently visited by humming-birds in 
South Brazil (Fritz Miiller, 359). My brother informs me by letter 
that it is also frequented by butterflies (Callidryas). 
Orv. MELASTOMACEL, 
_ Heeria, Schlecht., has: two kinds of stamens, one serving, 
apparently, to attract the fertilising-agents, and the other supplying 
_ the pollen for cross-fertilisation (606). 
Orv. LYTHRARIEL. 
165. LyTarum SanicartA, L.—This plant has acquired, through 
Darwin’s numerous and laborious experiments (158), so important 
