STRUCTURE AND FUNCTIONS OF THE POLLEN. 431 
Many observers have remarked the alterations which the 
form of the pollen frequently undergoes when placed in 
water. I find that the addition of acid often produces a 
fresh metamorphose. ‘Thus, in the Leguminose, Rosaceae, 
Crassulacee, Saxifragee, Hippocastanee, Rutacee, and those 
genera of Ranunculacee which have follicular fruits, the pol- 
len when dry is oval, and marked with a dark central line, 
but when placed in water, the central line disappears, and 
the figure rapidly becomes spheroid; again, when acid is 
added previous to protruding its contents, it usually assumes 
a triangular appearance. Now, it is very curious to find in 
- Grevillea, the pollen naturally to possess a triangular form, 
exactly similar to what acids produce in the former instances 
at the same time. This is beautifully explained in the struc- 
.ture of the flower in this genus; for the green stigma is very 
acid, and when the flower is young is pressed strongly against 
the anthers. The pollen being thus developed anüler acid 
influence, possesses normally the same Sem; as is apace’ 
in other cases artificially. 
The triangular pollen of Onagrarie aed Ciel, is at 
to be confounded with that of Grevillea, being produced bya 
very different cause. In the families cited, the triangular 
form of the pollen is produced by the cohesion of three 
spindle-shaped granules, which can be very distinctly seen in 
Epilobium hirsutum. In this species, each granule which 
enters into this compound pollen, is capable, under the influ- 
ence of acid, of dehiscing by a pore at each extremity, so 
that the pollen bursts by six pores. In Fuchsia, CEnothera, 
and Circea, the neighbouring pores coalesce, so that in these 
cases the pollen bursts by three pores only. 
A phenomenon, similar to that of Grevillea, is presented 
in Fumaria; in this instance the diadelphous stamens have 
‘their anthers collected between the extremity of the stigma 
and the connate and highly acid summits of the inner petals. 
Under these circumstances, the natural form of the pollen in 
-~ Fumaria is the same as may be produced through the poc d 
E Of acids in Corydalis and Dielytra. gi 
