Beer, Development of the pollen grain and anther of some Onagraceae. 293 
The name of „Zwischenkörper“, introduced by Fritsche, 
has been nsed by Nägeli and Strasbnrger in describing these 
pecnliar mucilaginous discs of the Onagraceous pollen grain. 
I shall speak of these discs as „interstitial bodies“ in the 
present paper. Three is the normal nnmber of interstitial bodies 
possessed by the pollen grains of all the species of Onagraceae 
which have been examined. In a few cases, however, I have 
noticed fonr or even live of these bodies whilst in others only 
two or one interstitial body occured (Figs. 21 and 22). An 
interesting abnormality has been noticed in some pollen grains 
of this age. Instead of the single nucleus which is normal at 
this time pollen grains have been seen which contain two nuclei: 
a large one and a small one (Fig. 18). The case is probably to 
be compared with the irregularities which Jnel 1 ) and others 
have described in the nuclear division of the pollen-mother-cells 
of Hemerocallis fulva and is no donbt due to one or more 
chromosomes becoming separated from the rest and forming an 
independent nucleus. 
There appears to be some Variation in the exact time when 
the special-mother-cell wall breaks down and sets free the pollen 
grains. A large nurnber of my preparations of 0. biennis show 
this to occur at the comparatively early age that we are now 
considering (viz pollen 22—24 g across). As was remarked 
above the first-formed laminae of the special-mother-cell wall 
maintain their individuality the longest and continue to give 
callose reactions for some time (Figs: 51 and 52). The rest of 
the wall now forms a homogeneous mucilage filling the pollen- 
sac and occupying all the spaces between the pollen-grains. It 
no longer has any affinity for corallin-soda and its reactions 
furnish no clue to its Chemical nature. 
As the pollen grains continue to develope the interstitial 
bodies become more prominent towards the exterior, giving the 
broader face of the grain a more pronounced triangulär outline. 
A secondary thickening layer is now formed within the 
first pollen wall. 
This layer extends over the whole inner face of the first 
membrane of the pollen grain. It runs up the sides of each 
interstitial body as a cylindrical extension which gradually thins 
off as it approaches the apex of the body and dies away alto- 
gether at the summit itself (see Figs. 19 and 23). The micro- 
chemical reactions of the thickening layer do not exactly corre- 
spond with those which are characteristic of any of the ordi- 
nary cell-wall components and its Chemical nature must for the 
present be left an open question. With a rather strong solution 
of lodine in potassium iodide it gives a very beautiful violet 
colour but with chlor-zinc-iodine and with a calcium-chloride 
solution of lodine it tinges only yellow or yellow-brown. Congo- 
9 Jxtel, 0. H., „Die Kernteilungen in den Pollenmutterzellen von 
Hemerocallis fulva etc.“ (Prings. Jalirb. f. wiss. Bot. XXX. 1897. p. 205.) 
20 
Beihefte Bot. Centralbl. Bd. XIX. Abt. I. Heft 2. 
