70 
Cutting.-- On the Pollination Mechanism of 
Strasburger has (in his paper ‘ Ueber den Ban und das Wachsthum 
der Zellhaute’ ( 15 )) described shortly the development of the walls of the 
pollen-grains of Thunbergia alata and T. reticulata. I hope to study the 
development of the peculiar exine of the Incarvilleas at some future date. 
All efforts to bring about the germination of the pollen-grains failed ; 
25 per cent, and 30 per cent, sugar solutions were tried, ordinary room 
temperatures and above room temperatures, up to 35 0 C., in the light and in 
the dark, and in some cases peptone was added to the sugar solution. 
Only the very first beginnings of a tube were noticed, and these were 
commoner at the higher temperatures, but did not persist in growing. 
At quite low temperatures, however, they were evidently able to germinate, 
in the open air, on the stigma of the plant, as when they were placed there 
the ovaries began to swell in a few days’ time and the fruit to ripen. 
I had but few fresh flowers to experiment with, and these had to be carefully 
conserved, so I could only make one preparation in sugar solution including 
a stigma, but even in these conditions the grains did not germinate properly. 
The moist-air method advocated recently by Anthony and Harlan ( 1 ) 
in the ‘ Journal of Agricultural Research ’ was also used, but with no favour- 
able result. When placed in the sugar solution the grains at once increase 
in size (Fig. 3, F) markedly, and some few (when the 25 per cent, solution 
was used) burst open. The slits widen, and by next day those grains that 
show the beginnings of germination have an irregular bulge coming from the 
portion of the intine lying between the openings of the exine. The walls of 
these bulges soon thicken considerably and growth stops. The intine, both 
of grains showing signs of germination and those that show no such 
indications, are very much swollen, and I am of the opinion that it is. this 
increase in size that stops the growth of the contents. 
Summary. 
A mechanical method of pollen-discharge is described in Incarvillea 
Delavayi , a plant possessed of a sensitive stigma. The pollen of the plant 
is dry, and is similar in structure to that of Thunbergia alata. The high 
osmotic pressure of the contents and the approximation of the walls of the 
surface slits, after drying, are regarded as adaptations to* prevent too great 
a loss of water in pollen transmission. 
Bibliography. 
1. Anthony, Stephen, and Harlan, H. V. : Germination of Barley Pollen. Journal of Agric. 
Research, vol. xviii, 1920. 
2. Bruck, W. : Over de prikkelbare Stempels van Torenia Fournieri en Mimulus lutens en over 
Voorbehoedmiddelen tegen het Kiemen van vreemd Stuifmeel op den Stempel. Versl. 
Wis.-Nat. Afd. K. Acad. Wet. Amst., x, 1902. 
