126 Gager . — The Development of the Pollinium and 
3 . Tetrads held together by the middle lamellae, which 
have been dissolved into mucilage ( Schleim ) without any 
special membrane structure for the individual pollen-grains 
in Orchis. It is a step further in the same direction when 
the middle lamellae between the tetrads remain unaltered. 
Whether this results in some Orchidaceae I know not, still 
one finds such a condition in several Mimosae (Rosanoff) and 
Acaciae (Engler), e. g. Acacia pulchella. In Asclepiadaceae 
(A. spec.) the reduction has proceeded still further, for here 
I have not succeeded in finding a single tetrad division, but 
the whole mass of apparently undivided pollen-mother-cells 
were surrounded by an exine-like membrane V 
Strasburger (1889), referring to Wille’s paper, also states 
that the pollen-mother-cell of Asclepias never divides. In 
A. syriaca , he says, one finds the single locule of each half 
of the anther filled with a row of large, radially oriented cells, 
rich in content, the primary mother-cells ( Urmutterzellen) of 
the pollen. These cells afterwards divide transversely, the 
longest lying in the middle of the locule, always dividing into 
four cells, those adjacent to its two walls into fewer cells, in 
some cases not at all 2 . 
Wille, then, seems to have been the first to suggest this 
interpretation of the structure of the pollinium in Asclepias. 
* Vines (1895) gives the same idea, stating that the pollen- 
mother-cells ‘ develop directly, without division, into a cell of 
the pollinium, each such cell being, at any rate physiologically, 
equivalent to a microspore.’ 
Later, Strasburger (1900) confirms Raciborski’s (1897) 
account of centrosome-like bodies in the pollen-mother-cell 
of Asclepias , but from the context it is not clear whether he 
there refers to the individual cells of the pollinium, or to the 
cell that gives rise to them, and, from the state of our know- 
ledge on the subject at the time Raciborski wrote, we cannot 
1 e Hier ist es mir nicht einmal gelungen, irgend eine Tetradentheilung zu 
finden, sondern ganze Massen scheinbar ungetheilter Pollenmutterzellen werden 
hier von einer eigenartigen Membran umgeben.’ Wille (1886), p. 41. 
2 ‘ Diese Zellen entsprechen den Pollenmutterzellen anderer Objecte, theilen 
sich aber nicht mehr.’ Strasburger (1889\ p. 80. 
