326 BOTANICAL GAZETTE [ NOVEMBER 
Chauveaud3 claims that the pollen mother cells of Cynanchum 
divide, but mentions only one division, with reduced number of 
chromosomes, the pollen grains forming from the daughter cells. 
Here one is left to infer that a mother cell formed only two 
microspores, or that there was a second division which escaped 
his observation. Wille+ examined Asclepias speciosa, but was 
unable to find tetrads. Strasburger’ finds no tetrad division in 
Asclepias Syriaca. He finds in the anthers what he terms sporog- 
enous cells, radially elongated, large, and rich in contents. 
These divide by cross walls into two, and the longest, near the 
middle of the sporangium, into four. He says the resulting cells 
are homologous with the pollen mother cells of other plants, 
and develop into microspores without further division. So far 
as I have been able to learn Zostera® and the Cynanchoideae 
are the only Angiosperms which are reported to form their 
pollen without tetrad divisions. It was thought that there were 
no tetrad divisions in the Cyperaceae until Juel? found that the 
nuclear division occurred, but no walls were formed. The 
reported different pollen formation in Cynanchum and Ascle- 
pias, the presence of tetrads in the Periplocoideae, and the 
small number of cases of pollen formation without tetrad 
division, all seem to warrant an investigation of the formation 
of microspores in the Cynanchoideae. 
In the spring of 1901 I undertook the task of looking into 
the pollen formation of some members of the Asclepiadaceae 
growing abundantly in the vicinity of Chicago. Those examined 
were Asclepias Cornuti, A. tuberosa, A. phytolaccoides, A. incarnata, 
A. verticillata, Acerates viridiflora, and A. longifolia. 
In A. Cornuti 1 was able to trace the development from the 
3 De la reproduction chez les dompte-venin 41. (Diss.) Paris, 1892. 
Paha gape die Entwickelungsgeschichte der Pollenkérner der Angiospermen 4I. 
5 Ueber das Wachsthum vyegetabilischer Zellhaute. Histologische Beitrige 2 : 80. 
° HOFMEISTER, Bot. Zeit. 10: 121. 1852. 
? Beitrage zur Kenntniss der bintovantned a eg Die Entwickelung der Pol- 
lenkGrner bei Carex. Jahrb. f. wiss. Bot. 58:6 ; 
