32 
FRED. ELFVING. 
to obtain tubes artificially. I then, sometimes successfully, 
tried to make preparations thereof out of the already fer- 
tilised pistils. 
The Pollen-tubes which I obtained in either way were 
immediately fixed with osmic acid or absolute alcohol. It 
is well to separate the moisture which surrounds the tube 
as much as possible before adding either of these reagents. 
This can easily be done with a capillary glass tube ; and 
thus powerful diffusion streams are avoided, which often 
occasion the bursting of the Pollen-tubes. The fixing then 
takes place almost instantaneously. 
The Orchids, especially those with richly-flowered spikes, 
offer splendid subjects for such investigations. I have ex- 
amined Orchis latifolia, 0. masculaj 0. maculata, Ophrys 
myodes, Platanthera hifolia, Gymnadenia conopsea, and 
Serapias francogallica, and am able to confirm the state- 
ments of Strasburger in every particular ; on which account 
I may for these simply refer to his drawings (1. c., p. 450, 452, 
plate t. xxvii, figs. 41 — 47). The formation and develop- 
ment of the Pollen-bodies corresponded exactly with these in 
every particular. The Pollen-body, originally provided with 
a round nucleus, is completely separated into two cells, of 
which the smaller is almost always to be found in one corner 
of the Pollen-body. The nuclei ^f these two sister-cells are 
round and almost of the same size ; the body of the nucleus 
of the smaller cell is, however, always smaller than that of 
the larger. No trace of a cellulose membrane between the 
two sister-cells could be detected, either by the use of 
reagents or by the crushing of the Pollen-body. Even the 
separating plasma-layer is removed at a later stage, and in 
the ripe Pollen-body the two nuclei lie free beside one 
another. 
The formation of the Pollen-tube takes a long time 
in the case of the Orchids, compared to that required by 
most other plants. Different species differ a little in this 
respect ; the best results were obtained, as a rule, by a culture 
of from twenty to forty hours, and in a solution of from 5 to 
10 per cent, of sugar. It proved to be, as Strasburger first 
found in these plants, that the nuclei wander together into 
the tube, and that in doing so the nucleus of the larger cell 
grows quite disproportionately. Both take a somewhat long 
elliptic shape. In tubes the results of older cultures, the 
anterior nucleus had elongated itself in a striking manner; 
the nucleolus was, however, to be seen clearly. I am 
inclined to regard this as only a change caused by cul- 
tivation ; because in tubes extracted from styles one always 
