IRRITABLE STAMENS 



563 



In the case of Oentawea Gyanus, the longitudinal walls of the 

 motor-cells are somewhat thicker than they are in C.jacea. According 

 to the author's observations, the thickest walls of all are found in 

 C. montana, where the motor- tissue closely resembles collenchyma 

 when viewed in transverse section (Fig. 2^9 c). 



The stout irritable staminal filaments of Herberts vulgaris, Mahonia 

 aquifolium and Opuntia vulgaris are also provided with a more or less 



030c 



Fig. 229. 



A. Part of a T.S. across a staminal filament of Centaurea jacca ; note the numerous 

 intercellular spaces in the motor-tissue. B. Peripheral region of a L.S. through a 

 similar filament. C. Small portion of a T.S. across a filament of C. montana. (All 

 the sections prepared from spirit-material.) 



thick- walled collenchyma-like motor-tissue, which is pervaded by narrow, 

 (Berberis) or wide (Opuntia) intercellular spaces. Slender irritable 

 stamens, on the other hand, such as those of Port ah tea grandiftora, 

 Abutilon striatum and Heliantheniurii vulgare, contain a thin-walled 

 motor-tissue. In Berberis, where the stamens always bend in the same 

 direction, i.e. towards the stigma, the motor-tissue is situated beneath 

 the papillose sensory epithelium (cf. Chap. XII.) on the adaxial (con- 

 cave) side of the filament. In other cases the tissue in question 

 generally occupies the whole of the available space between the epi- 

 dermis or the sensory epithelium and the central vascular strand. 



Motor-tissues may be stimulated indirect!}', through the mediation 

 of sense-organs, as in Berberis, Opuntia, Porfulaca and Abutilon, or 



