INSECT VISITORS 



137 



g. FloAvers pollinated by Small Insects (Sm). 



Hermann Miiller (' Alpenblumen,' pp. 510, 511) places in this category flowers 

 that are visited and cross-pollinated by small insects belonging to various orders. 

 Herminium Monorchis may be named as a type of the group. Its minute greenish- 

 yellow flowers, possessing, however, a powerful odour, were observed by George 

 Darwin to be visited by equally small Hymenoptera, Diptera, and Coleoptera, while 

 Hermann Miiller adds tiny Ichneumons (Braconidae and Pteromalidae) to the list 

 of visitors. When these little creatures, which are only i-i\ mm. long, creep 



Fig. 53. Hermiiniiin Mouorchis, R.Br., a Small-insect Flower (after Heniiann MuIIer). A. Flower 

 seen from the right side (x 7). B. The same with floral leaves completely spread out, seen from the front. 

 C. The same showing; the natural position of the parts as seen from the left side. D. Pollinia (x 32). 

 E. Sexual organs and base of the labellum (x 32). s, Outer perianth leaves; p, inner perianth leaves; 

 a, anther-lobes ; a', vestiges of the other stamens ; si, lobes of the stigma ; ov, ovary ; sp, spur ; br, bract ; 

 k/, rostellum ; x, under-side of the same. 



into the flower (in the direction of the arrow in Fig. 53), and linger at the nectary, 

 the pollinia get cemented to them, and are carried to the stigma of the next flower 

 visited. 



Perhaps Chamaeorchis alpina, which has already been mentioned (see p. 122) 

 among the Ichneumon Flowers, would more properly be placed in the present 

 group. 



IX. Insects that visit Flowers. 



If not only the Colour of flowers, but also their Odour serves as an allurement 

 to insects eff"ecting cross-pollination, these insects must possess well-developed 

 olfactory orgatis, as well as acute organs of sight. There are, in fact, many indica- 

 tions that their antennae are the seat of the olfactory sense. The sensory structures 

 here occurring are either confined to the ends of individual joints, sometimes the 



