Band 138. Nr. 21. XXXIX. Jahrgang. IL Bd. Nr. 21. 



Botanisches Oentralblatt 



Referierendes Organ 



der 



Association Internationale des Botanistes 

 für das Gesamtgebiet der Botanik. 



Herausgegeben unter der Leitung 



des Präsidenten • des Vice- Präsidenten : des Secretärs: 



Dr. D. H. Scott. Prof. Dr. Wm. Trelease. Dr. J. P. Lots?. 



und der Redactions-Commissions- Mitglieder : 



Prof. Dr. Wm. Trelease, Dr. C. Bonaventura, A. D. Cotton, 



Prof. Dr. C. Wehmer und Mag. C. Christensen. 



von zahlreichen Specialredacteuren in den verschiedenen Ländern. 



Dr. J. P. Lotsy, Chefredacteur. 



No. 47. 



Abonnement für das halbe Jahr 15 Mark 

 durch alle Buchhandlungen und Postanstalten. 



1918. 



Alle für die Redaction bestimmten Sendungen sind zu richten an: 

 Re daction des Botanischen Centralblattes, Haarlem (Holland), Spaarne 17. 



Payson. E., The pollination of Asclepias cryptoceras. (Bot. Gaz. 

 LXI. p. 72—74. 1916.) 



The general mechanism of an Asclepiad flower is well known 

 and is onty briefly recapitulated in the present paper. The "jewel 

 milkweed" {Asclepias cryptoceras) differs from the typical asclepiad 

 in several important respects. The flowers are nodding instead of 

 erect, and, as a direct adaptation to this, the hoods are closed 

 except for a small opening at the apex; the hörn is small and in- 

 cluded or hidden within the hood; the lips of the slit are firmly 

 closed, and instead of offering an easy entrance to their trap seem 

 to make the entrance difficult. In many kinds of milkweed the 

 hoods and the upper part of the column are borne on a pedicel 

 several millimeters in lenght. The hoods are sessile in Asclepias 

 cryptoceras. 



Th'e pollination of the jewel milkweed, in southwestern Colo- 

 rado at least, is apparently accomplished by only one species of 

 insect, Bombus Morrisoni Cressn., a bumblebee. This bee is a füll 

 match for the large flower, yet it has a rather difficult time obtain- 

 ing the nectar. Since the flowers are nodding and since the pedicel 

 is absent, there are no footholds offered, and the bumblebee must 

 continually scramble to keep its position. The hoods guide its feet 

 to the slits, and the bee forces them open, and in order to free 

 itself loosens the corpusculum and drags out the pollinia firmly 

 fastened to its feet. When they dry they are in a convenient posi- 

 tion to enter the next slit that chances to open in the bee's scram- 

 bling for a foothold. 



The fragrance of the flowers is so intense that one would ima- 



Botan. Oentralblatt. Band 13S. 1»18. 21 



