DEVELOPMENT OF THE POLLEN IN SOME 
ASCLEPIADACEAE 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY, 
XXXII. 
T. C. FRYE. 
(WITH PLATE XIII) 
It 1s well known that in the Cynanchoideae’ the microspores 
of each sporangium adhere in a mass, forming what is known as 
apollintum. This is true also of some of the Orchidaceae and 
Leguminosae. Since the three families mentioned are all highly 
specialized for insect pollination, the adherence of pollen may 
perhaps be regarded as having no special morphological signifi- 
cance. The Asclepiadaceae are further exceptional in the 
production of only two sporangia in each stamen. In the 
Balanophoraceae, Orchidaceae, and Mimosoideae, the number of 
microsporangia is variable. The large number in some of the 
Mimosoideae is attributed to the interjection of plates of sterile 
tissue. In the same way Lemna minor is said to form four, the 
normal number, from a single mass of archesporial tissue. The 
question arises whether, in the Cynanchoideae, there is any indi- 
cation of suppression or fusion of sporangia in the earliest 
stages of their development. More interesting does this become 
when we recall that in the small group Secamoneae the pollinium 
in each half anther is paired, but the parts adhere closely. 
Little is known about the formation of pollen in the Ascle- 
Piadaceae. In the Periplocoideae tetrads are formed, the micro- 
Spores adhering in groups of four when mature. Of the pollen 
development in the Cynanchoideae almost nothing is known. 
*The author follows the classification of Engler and Prantl in Dye nattirlichen 
Phlanzenfamilien. 
= * CALDWELL, O. W., Onthe life history of Lemna minor, Bort. GAZ. 27 : 37-66. 
99. 
1901] : 325 
