402 THE FERTILISATION OF FLOWERS. [PART III. 
its proboscis, held fast thus by a bristle, it tears away the corpuscu- 
lum and its two pollinia; and the pollinia and the processes which 
carry them, both of which were hitherto kept moist beneath the 
anthers, are now brought for the first time into the open air, and 
begin to be dried up. In consequence of this, the processes, which 
previously stood out in opposite directions, now bend so that the 
pollinia come close together, face to face. If the fly now inserts 
its proboscis into another nectary on the same flower, it will be in 
a slightly different position with regard to the slit in the case of 
each different nectary, and for this reason alone the same bristle 
will not be caught. Besides, it is a considerable time before 
the processes are so far dried that both pollinia of the same 
corpusculum can be inserted into the slit along with the bristle 
that they are attached to, so that, as a rule, the fly has mean- 
while flown away to another plant. Here, if a proboscis-bristle 
bearing pollinia (which has.now become closely approximated) gets — 
again caught in the slit, one (or both) of the pollinia slides into 
the stigmatic chamber which lies behind the slit, and remaims — 
sticking in it, torn away from the process that attached it to the 
corpusculum. So crossing of separate flowers, and for the most 
part of separate plants, is rogulanby effected. Other visitors besides 
carrion-loving flies (¢.g. Hmpis, Polistes), occasionally attach one or 
more corpuscula to the tips of their proboscides, but can scarcely 
ever effect cross-fertilisation (609). 
Hoya globulosa.—Myr. Worthington Smith has recently given a 
minute description of the fertilisation of this flower (699). He states 
that the corpuscular processes (retinacula) are elastic! When in~ 
the flower they are like an extended spring, but the instant the 
pollinia are withdrawn the spring closes, and the two pollinia quickly — 
cross each other and hold tightly on to the insect’s foot. The flower 
is distinctly proterandrous, 
Darwin describes a very remarkable instance of Hoya carnosa 
bearing cleistogamic flowers in cultivation (167). | 
Stapelia also has cleistogamic flowers, according to Kuhn (399). 
Periploca greca, L.—The mode of fertilisation has been described 
by Delpino (172, 352). 
Orv. GENTIANEL. 
Gentiana lutea, L.—The honey is freely exposed, and I have 
found the plant visited by twenty-seven species of mostly short- 
lipped insects. The flower is homogamous, and self-fertilisation is 
not impossible (570, vol. xv. ; 609). . 
