354 RIKARD STERNER 



which Cynanchum takes in the matter of dispersal in the flora of rocky escarp- 

 ments, seems to me to be remarkable from this point of view. 



In order to obtain some definite knowledge with regard to the dispersal of 

 the species by means of the seed, comprehensive researches were set on foot in 

 the latter part of last summer as regards the formation of fruit and seed. These 

 researches must, of course, be continued for some years in order to yield satis- 

 factory evidence. The results so far are as follows: — 



In the interior part of southern Tjust and in the south-east of Ostergotland 

 I found that the formation of fruit was quite insignificant. In most localities I 

 sought in vain for anything of the kind, while the numerous flower-stalks that 

 remained bore witness to an abundant blossoming. In Sodermanland and Upp- 

 land the formation of fruit varied greatly. As a rule it may be said that on 

 open localities, especially high rocky escarpments, there was little or no forma- 

 tion of fruit; on localities in a more sheltered position, as on the low rocky 

 humps in ploughlands or moraine hillocks, on the other hand, the formation of 

 fruit could be regarded as fairly good. The richest formation of fruit had taken 

 place in localities which lay in the neighbourhood of barns or adjacent to 

 roads with a heavy traffic. 



These circumstances are in good accordance with the account of the pollina- 

 tion biology of Cynanchum which is to be obtained in the textbooks (e. g. 

 Kirchner 191 1, pp. 216 ff.). The Cynanchum flower can be pollinated only by 

 certain large flies which have strength enough to tear away the pollinia and 

 carry them off" (Anthomyia, Pyrellia, Sarcophaga, Onesia, and Tachina). These 

 flies naturally thrive less well on rocky cliffs exposed to the wind than on low- 

 lying shore-slopes and hillocks; and the flies would appear in greatest numbers 

 in the neighbourhood of barns and highroads. 



The occurrences of Cynanchum in the interior of the country, especially those 

 lying high above sea-level, are chiefly found in rocky cliffs. That the dispersal 

 of the species further inland is so insignificant, therefore, is probably explained 

 by the pollination biology of the plant and the nature of the localities. 



These researches have also comprised the formation of seed. This last varied 

 greatly, and the material before me does not supply a safe basis for a judgement 

 as to the causes of this fact. To a very great extent the seeds were destroyed 

 by insects (according to information kindly given me by Professor Ivar Tragardh, 

 probably by a fly, Ortalis connexa), or else they had for some other unknown 

 cause come to nought, killed in an early stage, shrunken and empty. Possibly 

 sometimes shortage of water may be a cause why the seeds do not develop. 

 In most cases, however, the plant as to the rest showed no '^traces of suffering 

 from drought. — Geisenheyner (1904), who has studied the biology of Cynanchum 

 in Brandenburg, has, as to that area, too, reported a feeble formation of fruit, a 



