780 SUMMARY OF CURRENT RESEARCHES RELATING TO 



are contrived for Apidse and Lepidoptera with a longer or shorter pro- 

 boscis. Of trilateral actinomorphic flowers an example occurs in Iris, 

 with adaptation to the visits of the larger Apidse, such as Bomhus, &c., and 

 the same is the case with the bilateral flowers of Dicentra, probably similar 

 to the primitive type of the nearly allied Cruciferse. 



Monocentric actinomorphic or suhzygomorphic flowers are those with 

 a longer or shorter tube, visibly adapted to insects furnished with a 

 proboscis. Lychnis dioica and some species of Clerodendron may be cited 

 as examples. 



The very numerous unilateral zygomorphic flowers may be again 

 classified, either according to the region of the visiting insect which 

 becomes pollinated, as nototribal, sternotribal, and pleurotribal, or accord- 

 ing to the class to which the visiting insect (or bird) belongs, as melitto- 

 philous, sphyngophilous, or ornithophilous. Nototribal melittophilous flowers 

 include the Labiatse, Scrophulariaceee, Bignoniacese, &c. ; nototribal 

 ornithophilous flowers are exclusively exotic. Among the sternotribal 

 melittophilous are included the greater part of Papilionacese, Viola, Rhodo- 

 dendron, &c. ; Amaryllis formosissima is sternotribal and ornithophilous ; 

 Lilium longijlorum and Funckia sternotribal and sphyngophilous. Zygo- 

 morphic pleurotribal flowers are almost entirely melittophilous, such as 

 Poly galeae, some Papilionacea?, &c. 



In those families in which zygomorphy is most strongly pronounced, 

 there is scarcely a single instance of anemophilous flowers. 



Origin of Zygomorphic Flowers.* — Herr W. 0. Focke suggests a 

 probable origin of zygomorphic flowers from a comparison with those 

 whorls of leaves, such as those of Catalpa syringsefolia, where one leaf in 

 the whorl is more fully developed than the others, viz. the one which is 

 most exposed to air and light. He calls attention to two specially marked 

 types of zygomorphy, viz. : — (1) The Leguminosse-type, which appears to 

 have originated in a curvature of the style causing the concave side to be 

 directed upwards, and which may be the simple result of light-irritation ; 

 the petals are here quite distinct or only slightly coherent at the base ; to 

 this type belong, besides the Leguminosse, some Amaryllideae, Ghryso- 

 balaneae, and Geraniacese. (2) The Labiatae-type, where the corolla is 

 distinctly gamopetalous, often two-lipped, and the stamens have a tendency 

 to become didynamous ; to this type belong the Lobeliacese, Caprifoliacese, 

 BignoniaceaB, Scrophulariaceee, and Labiatse, with a modified form in the 

 Composit^e. Besides these are several other less clearly marked types, the 

 origin of which is not so clear. 



Conduction of Irritation in irritable stigmas, f — Mr. F. W. Oliver 

 has investigated the mode of conduction of the irritation in the stigmas of 

 Martynia lutea and prdboscidea and Mimulus luteus and cardinalis, and 

 believes it to be due to the continuity of the protoplasm from cell to cell, 

 which he was able to demonstrate by Gardiner's method of sulphuric acid 

 and Hoffmann's blue. 



In both the genera mentioned, the tissue of the stigma consists of two 

 lamellae which are sensitive to contact on the inner side only. The internal 

 tissue of the lamellae is composed of 15 to 20 layers of excessively thin- 

 walled prismatic cells with a great development of intercellular spaces. 

 Between the upper and lower epidermis of the lamellae runs a simple axile 

 vascular bundle of spirally thickened tracheids. The bundles from the 

 two stigmas do not unite before they reach the ovary. The irritability is 



* Oesterr. Bot. Zeitschr., xxxvii. (1887) pp. 123-6, 157-61. Of. this Journal, ante, 

 p. 266. t Ber. Deutsch. Bot. Gesell, v. (1887) pp. 162-9 (2 figs.). 



