VOL. XII. NO. 42.—BOTANICAL GAZETTE DC. 1887: 
Three nuclei in pollen grains. 
BYRON D. HALSTED. 
(WITH PLATE XVI.) 
_The pollen under consideration was obtained by placing 
twigs of Sambucus racemosa in a tall bell jar of water on 
March 3d and keeping them in a warm sunny room, The 
€xperiment was begun primarily to illustrate to students the 
effect of coating the cut surface of the severed twig with 
asphalt or a similar substance impervious to water. There 
Were four similar twigs, each eighteen inches long, placed 
In the water. Two of them had. their cut surfaces coated 
‘with varnish, while the remaining two were set in the liquid © 
With the freshly cut ends fully exposed. The asphalt used 
Was that employed for cementing cover glasses to the slides 
in making permanent microscopic preparations. The buds 
upon the stems having free cut surfaces quickly began to 
enlarge, while those of the twigs that had received the var- 
nish did nothing more than slightly swell, and never produced 
a 
teristic foliage, and at three of the nodes flower clusters of 
upon the shrubs several weeks later in the season. 
‘hen viewed dry, the pollen is about twice as long as 
broad (20 » by 40 »), and exhibits three dark lines or sutures 
Which run lengthwise of the grain. The appearance of the 
dry grains is shown at a@ in the plate. All the illustrations 
were drawn with the camera to the same scale, and are mag- 
nified two’ hundred and eighty times. To the left of Z are 
two grains showing the surface of the dry grains. The 
€xtine is marked with faint irregular lines, resembling a net- 
ork of minute cells. This slight obstruction to the view 
‘maa disappears when water is added, and at the same 
