246 



ANGIOSPERMAE—DICOTYLEDONES 



and placed almost at the same level, but sometimes they project a little beyond them. 

 In such cases cross-pollination is likely to result from insect-visits. As the stamens 

 closely surround the style, and the anthers dehisce introrsely, the sticky pollen — 

 owing to the pendulous nature of the flower — readily falls upon the stigma. 



Visitors. — In the Kiel Botanic Garden, I observed only the following Diptera, 

 skg. or po-dvg. — (a) Syrphidae: i. Eristalis tenax Z.; 2. Syrphus ribesii Z. ; 3. 

 Melanostoma mellina Z. (V) Muscidae : 4. Scatophaga stercoraria Z. ; 5. Lucilia 

 caesar Z.; 6. Sarcophaga carnaria Z. 



XXIX. ORDER RHAMNEAE R. BR. 



Inconspicuous protandrous flowers, with exposed nectar. Dioecism frequent, 

 dimorphism occasional. 



185. Rhamnus L. 



Inconspicuous, frequently dioecious flowers with exposed nectar secreted by the 

 calyx. In some species there are dimorphous flowers (e. g. R. lanceolata, according 

 to Darwin). 



Fig. 75. Rhamnus pumUa,L. (After Herm. Mailer.) ^. A tetramerous flower with two petals; 

 two anthers have dehisced, and two have not. B. A tetramerous flower without any petals ; all the 

 anthers have dehisced. C. A pentamerous flower with Ove petals ; all the anthers have dehisced. D. The 

 same in longitudinal section. 



616. R. cathartica L. (MacLeod, Bot. Jaarb. Dodonaea, Ghent, vi, 1894, 

 pp. 248-9; Schulz, 'Beitrage,' II, p. 185; Kirchner, 'Flora v. Stuttgart,' p. 363; 



Wamstorf, Verb. bot. Ver., Berlin, xxxviii, 1896 ; Knuth, ' Bloemenbiol. Bijdragen.') 



Kirchner states that in this species each kind of the greenish, dioecious, fragrant 

 flowers possesses vestiges of the opposite sex-organs. The male flowers are larger 

 than the female : their pistil is either quite rudimentary, and devoid of stigma, or 

 it may be somewhat better developed. The female flowers possess vestigial stamens 

 and are dimorphous. 



According to Wamstorf, shrubs with pseudo-hermaphrodite pollen-flowers are 

 rare at Ruppin and flower more freely than the female stocks. The petals only 

 cover the filaments of the four stiff, erect stamens ; the anthers dehisce introrsely. 

 The pollen-grains are white, spheroidal, ellipsoidal, or ovoid, on an average 31 « 

 long and 25 yn broad. 



