430 



KNOWLEDGE. 



November, 1911- 



gives it its name), owing to the 

 secretion formed within the hairs. 

 Those people who have e\-er had 

 the handhng of Jerusalem Arti- 

 choke plants will know that their 

 leaves are extremeh" rough, but 

 'few of them know that this fact 

 is owing to the presence of count- 

 less m}riads of sharp-tipped, 

 jointed hairs that are, if any- 

 thing, even more rough than 

 those of the Harpaliiini. a plant 

 of the same natural order. It 

 needs but a microscojie to show 

 the bristling, scabrous upper 

 coats of these simple, jointed 

 structures, and we can then 

 easily understand wh\' the leaves 



Figure 7. 



Jointed Hair from the leaf veins of 

 Pineapple Sage. 



Scented Geranium. It is owing 

 to the presence of these hairs on 

 this plant that we get the 

 delicious odour when the leaves 

 and stems are pressed, for the 

 hairs are glandular, but of so 

 distinct a form that they are 

 classed b\' themselves as the 

 "clubbed,"" Figure 11 clearh- 

 shows some from the stem of the 

 Geranium, and one can note the 

 simple {i.e.. unbranched), thick- 

 coated hairs, each of which is 

 just like a club standing up on 

 a curious swollen base. They 

 are verv pretty objects both in- 

 dividually and in the mass, and 

 perhaps the fact that they are 



Figure 8. Jointed Hairs from the cal\x of Purple Dead Nettle. Figure 9. Jointed Hairs from the stem of Harpalinm. 



feel so rough and unpleasant to the touch. 

 Clubbed hairs are \-er\- often known as 

 Clavate. or club-shaped, and are so marked 

 in their features that it is difficult to overlook 

 them even when they grow — as is often the 

 case — in compan\' with masses of ordinar\- 

 ong and simple, or other forms of hair\' 

 appendages. Some very nice examples ma\- 

 :ie seen in the White Campion and Pansy ; 

 in .\vens and the interior of Willow-galls, 

 and so on, but one of the best plants is the 



comparati\"el\- iinccimnKm makes them all 

 the more interesting when we come 

 across them, as is often the case, uncon- 

 sciously : for \'ery often one kind of hair 

 is met with exclusively on a plant, 

 but at other times one nvdv suddenh' 

 come across another kind interspersed 

 just here and there, and no more. In 

 this uncertaint\" lies the charm of real 

 obser\"ation work, be it with the naked 

 eye or microscope. 



I'IGURE 10. 



Jointed Hair from the stem 



of Mouse-ear Chiclvweed. 



Figure 11. Chibl)ed Hairs from the stem of Scented Geranimi 



Figure 12. 



Jointed Hair from the edge 



of Jerusalem Artichoke. 



