SENSITIVENESS AND IKRITABILITY OF PLANT ORGANS. 163 



There is no need to describe a long series of movements, 

 my object being simply to emphasize the fact that sensitive- 

 ness and irritability are pronounced phenomena in flowers, 

 which point to a highly irritable condition of the protoplasm 

 contained in the cells of all the floral members.* And, although 

 we cannot now trace the progress of change in the floral 

 organs under the mechanical and physiological impulses due 

 to insect agency, the probability that these have been the 

 actual influences to which the tissues have responded, and 

 thence evolved the existing floral structures, will now, I trust, 

 appear to the reader to be of a very high order. 



of the irritation in the stigmas of Martynia lutea and M. prohoscidea, and 

 of Mimulus lufeus and M. cardinalis. He believes it to be due to the 

 continuity of the protoplasm from cell to cell. The tissue of the stigma 

 consists of two lamellae. The irritability is confined to sevei*al layers 

 of prismatic cells on the inner side of the lamella, where the continuity 

 of protoplasm was determined. (Quoted from Journ. Boy. Micr. Soc, 

 1887, p. 781. Ber. Deutsch. Bot. Gesell., v. (1887), p. 162.) 



Mr. Oliver has also lately contributed a valuable paper to the Annals 

 of Botany (vol. i., p. 237, pi. xii., 1888), on " The Sensitive Labellum of 

 Masdevallia muscosa." Continuity of the protoplasm occurs in the irritable 

 "crest" on the labellum, which rapidly rises on being touched; the 

 mechanism being closely comparable with that of the pulvinus of Mimosa. 

 The author corroborates Mr. Gardiner's observation that a large amount 

 of tannin occurs in the cells with which such irritability is concerned. 

 References are also given to descriptions of other Orchids remarkable 

 for having irritable perianths. 



* For further information on the effects of light and heat upon the 

 opening and closing of flowers, the reader is referred to Sachs' 

 Physiology of Plants, chap, xxxvi., p. 641, where the author gives an 

 account of Pfeffer's investigations. It is not clear, however, how 

 temperature acts. A casual discovery may perhaps supply a hint. On 

 forcing air into the flower-stalk of the white Water-lily, I found that the 

 petals instantly spread open. May not, therefore, a rise of temperature 

 cause the air within the tissues to expand, and so at least help to produce 

 the same effect ? 



