CUCURBITACEAE 457 



the column of filaments rises to a height of 1 mm. It is 2 mm. in diameter, and 

 bears at its apex the united and convoluted anthers, as a rounded mass. Dehiscence 

 takes place in the mature bud. 



The female flowers are considerably smaller than the male ones, and are 

 arranged in heads of fifteen to twenty flowers, these too being less conspicuous 

 than the male inflorescences. The latter are therefore (as Sprengel emphasized 

 for Bryonia alba Z.) usually the first to be noticed and visited by insects, and it 

 is not till they are done with that the less easily observed female flowers receive 

 attention. All the female flowers of an inflorescence mature simultaneously. It 

 is therefore possible or even probable that all may be crossed with the pollen 

 brought at a single insect-visit. The diameter of the female flower is only 4-5 mm. 

 In the middle of the five petals, which resemble those of the male flowers, the style 

 projects to a height of 2 mm. from a small secretory disk. It terminates in three 

 capitate stigmas. These occupy the entrance to the flower, so that a nectar-seeking 

 insect must inevitably touch and pollinate them if it has previously visited a male 

 flower. The large number of visitors to these inconspicuous greenish flowers, as 

 well as their strong action (like those of Bryonia dioica Z.) on photographic plates, 

 suggested to me that they may possess means of attraction invisible to human 

 eyes though perceptible to those of insects. I expressed the view that the flower 

 pigment of Sicyos (and also of Bryonia) emits ultra-violet rays ; but it is also 

 possible that the marked effect upon photographic plates is due to reflection of 

 light by the numerous glands which cover the flowers (cf. Vol. I, pp. 87-8 ; and 

 Nos. 1742, 1743, 1747, in the Bibliography, Vol. I, pp. 285-6). 



Visitors. I observed the following, all freq., skg. a bee (Apis mellifica Z.), 

 a wasp (Vespa vulgaris Z.), and 6 flies (Eristalis nemofum Z. ; Lucilia caesar Z. , 

 Onesia sepulcralis Z. ; Sarcophaga carnaria Z. ; Sepsis cynipsea Z. ; Syrphus 

 ribesii Z.). 



314. Cucumis L. 



Large yellow monoecious flowers, with the same mechanism as Bryonia. 

 Two pairs of filaments are united, the fifth is free. The anthers converge. 



1082. C. sativus L. (Sprengel, ' Entd. Geh.,' p. 435.) In this species again 

 the male flowers are much larger than the female ones, and are therefore usually 

 visited first. 



According to the researches of F. Noll, this species, like the fig and Mespilus 

 germanica, var. apyrena Koch, can produce ripe but seedless fruits without pollination 

 (parthenocarpy). (Verh. nathist. Ver., Bonn, 1902.) 



Visitors. I only observed the honey-bee, skg., at Kiel (' Bloemenbiol. Bij- 

 dragen'). 



Sickmann records the fossorial wasp Crabro brevis v. d. Z. for Osnabruck, 

 very common. 



1083. C. Melo L. (Aubert, J. soc. horticul. France, Paris, Ser. 3, iii, 1881, 

 p. 233.) Aubert states that the first female flowers of this species open five to six 

 days after the first male ones, and that the latter are much more numerous. The 

 results of artificial fertilization are seen in two to three days, and the first ripe fruits 

 appear after seven to eight weeks. 



