IRRITABLE STAMENS. 



651 



more or less numerous small flowers are situated on a common broad floral 

 receptacle, surrounded by an involucre of many small leaves : the whole 

 impresses the non-botanical observer as a single flower. Those not skilled in 

 botanical matters will easily see their way when I add that the common blue 

 Corn Flower and its allies {Centatirea), the common Thistle {Carduus) and the 

 well-known Artichoke {Cynara), together with many other genera, belong to the 

 Cynarese. Each individual floret contained in the flower-head of these plants 

 consists of an inferior ovary, from which rises a long narrow flower-tube which 

 suddenly opens out above, assuming the form of a bell, the margin of which has five 

 spreading teeth. At the place where this widening of the corolla occurs five stamens 

 arise, the anthers or pollen-sacs of which are in aU Compositce so coherent laterally 

 that they form a tube, through which the upper part of 

 the style projects, arising from the inferior ovary at the 

 base of the corolla-tube. 



Now the five stamens referred to are the objects with 

 which we have to do here\ These are fixed by their 

 lower ends to the corolla-tube, as shown in Fig. 374, and 

 at the upper end to the tube formed by the anthers. 

 Left to themselves, and before the emptying of the pollen 

 from the anthers, the five stamens are strongly curved 

 convexly outwards. If one of them is touched, as with 

 the point of a blunt needle, it extends itself straight, 

 i. e. it becomes proportionally shorter ; it may then 

 happen that, in consequence of the curvature experienced 

 by the style passing between the stamens, the other 

 stamens also become dragged or pressed on to the corolla- 

 tube, and this acts on them as a stimulus, whence they 

 also contract, and the anther-tube with the style going 

 through it becomes curved towards the other side again. 

 The whole sexual apparatus of such a tubular flower may 

 thus be put into a condition of pendulous movement to and fro. 



For the purpose of more exact studies it is well to take single florets out of the 

 capitulum, and to cut away the corolla down to the origin of the filaments, or 

 to cut across the corolla-tube, stamens and style, above the insertion of the 

 filaments, and fix the freed sexual apparatus in damp air by means of a needle. 

 When the filaments have recovered from the stimulation due to the operation, they 

 stand sufficiently convex outwards — concave towards the style — for free movement. 

 The filaments are not round : the radial diameter (with reference to the flower) is 

 considerably smaller than the tangential one. Each consists of an envelope of 

 3-4 layers of long, cylindrical parenchyma cells, separated by thin straight trans- 

 verse walls, and surrounded by a layer of similarly shaped epidermis-cells (with 

 a strong cuticle), which in many places grow out into hairs, each of which is 



Fir,. 374. — Stamens of Centatirea 

 jact-a freed by removal of the corolla. 

 --/ in tlie non-irritated, B in the con- 

 tracted state (magnified), C corolla, 

 tube ; s filaments ; a anthers coherent 

 into a tube ; ^ style. 



' As to the stamens of the Cynarece, the reader may compare, in addition to Pfcffer's work 

 already quoted, Franz linger, ' L'ber die S/ni/ctiir einiger reizbaren P/innzenf/ieile," Bot. Zeit., 1872 

 (p. 113)- 



