366 



A NGIOSPERMAEDICOTYLEDONES 



Fig. 361. Euphorbia, L. (from nature). 

 (1) E. Pepius, Z,., in the first (female) stage ; the 

 stigmas project a little from the involacre. (3) 

 E. Helioscapia, L., in the second (male) stage ; 

 the ovary (the female flower) with its non-receptive 

 stigmas hangs far out on a curved stalk: the 

 stamens (male flowers) protrude from the in- 

 volucre. 



branchlet. This is composed of several (10-12) male flowers (each consisting of 



a single- stalked stamen) with a central female flower, and is surrounded by a calyciform 



involucre with a four- to five-lobed limb. 

 ^ The glands of this investment secrete 



shallow layer of completely exposed nectaril 

 This inflorescence, oecologically equiva- 

 lent to a single flower, is strongly proto- 

 gynous {cf. E. palustris Z.). The three 

 bilobed stigmas emerge first from the in- 

 volucre, and may be dusted with foreign 

 pollen if insects visit the flowers. Later, 

 when the ovary (on a long, curved stem) 

 projects far beyond the involucre, the stamens 

 gradually elongate one after another, dehiscing 

 at the same time, and take the place which 

 was occupied in the first stage by the 

 stigmas. Pollination is effected exclusively 

 by flies, but beetles and wasps are occasional 

 visitors, and, in places where the plants grow 

 in large numbers close together, bees may 

 also be observed. 

 Kemer states that the anthers close in damp air and open again when it is dry. 



Jordan observed that they turn their pollen-covered sides to the flower entrances 



above the nectaries. 



2521. . helioscopia L. 



Visitors. The following were recorded by the observers, and for the localities 

 stated. 



Herm. Miiller, Anthomyia sp. and other flies. Knuth ('Bl. u. Insekt. a. d. 

 nordfr. Ins.,' p. 167), 5 'Dip\.er2L{a) Musa'dae : 1. Anthomyia sp. {b) Syrphidae: 

 2. Melanostoma mellina Z. ; 3. Syritta pipiens Z. ; 4. Syrphus balteatus Deg. 

 (f) Tipulidae: 5. Pachyrhina sp. Knuth (Helgoland, Bot. Jaarb. Dodonaea, Ghent, 

 viii, 1896, p. 36), 5 Diptera (a) Muscidae: i. Coelopa frigida Fall.\ 2. Fucellia 

 fucorum Fall. ; 3. Lucilia caesar Z. (3) Syrphidae : 4. Chrysotoxum festivum Z. S ; 

 5. Eristalis tenax Z. MacLeod (Flanders, op. cit., vi, 1894, p. 379), 2 hover-flies. 

 Plateau (Flanders), a bee (Proscopis sp.) and a hover-fly (Syrphus corollae F). 

 Schletterer (Pola), a bee (Halictus calceatus Scopi), a Sphegid (Salius fuscus F\ and 

 a saw-fly (Arge cyaneocrocea Fbrst.). Delpino, only flies. 



2522. E. verrucosa Lam. 



Visitors. Loew (Berlin Botanic Garden) observed a Muscid (Lucilia caesar Z.) 

 and 2 hover-flies (Ascia podagrica F., and Eristalis nemonim Z.) (' Bliitenbiol. 

 Floristik,' p. 332). 



2523. E. Gerardiana Jacq. 

 Visitors. The following were recorded by the observers, and for the localities 



stated. 



Loew (Berlin Botanic Garden, loc. cit,), the honey-bee and a fossorial wasp 

 (Crabro lapidarius Pz. 5). Plateau (Ghent), 3 flies i. Eristalis arbustorum Z. j 



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