November, 1911. 



KNOWLEDGE. 



429 



possesses a number of species specialh- noted for the 

 ■■ felt " on the under-surfaces of their leaves, stems, 

 and so on. If only one be selected for e.xamination, 

 say the pretty little Mouse-ear Hawkweed, this one 

 plant will afford much that will interest us, for the 

 starfish-like hairs which form the "" felt " are the 

 most fascinating' objects. Figure 1 represents some 

 of them from the involucral bracts of the flower- 

 head, but the lea\'es and stems of this plant art- also 

 covered with thi' same i)rett\- silver\- structures. 



Front View. 



Side View. 



Figure 4. 

 late Hairs from the flower pedicels of I\\-. 



and other lii\el\- 



[eaves and stem of 



amongst the Mallows : in the curious 



and in a 

 1 iilants. 



\ery delicate and ver\' chaste 



examples may be found on the 



HolK'hock 



growths called '"Oak spangles" or "galls,' 



great many other common garden and wi 



It is difficult to say why hairs 

 should become " stellate," }-et one can 

 see that their form is well adapted 

 for the forming of "down" or felt- 

 like growths, whicli no doubt play 

 an important part in the protection 

 of plant-surfaces. 



Strange as are the stellate, the 

 jieltate or shield-like are. perhaps, the 

 most curious of all the man\- different 

 hairs with which we meet. Their I'' 



appearance on a plant often causes 

 the surface on which the\- spring to look, and feel, 

 ver)- scurfy and roughh' scalw for which reason the 

 term " lepidote " has been given to such hairs, 

 the word " lepis " being another name for "scurf." 



Such a hair as this grow, from the e[)idermis 

 of leaf, stem, and so on. in such a w'a\' tliat it is 

 attached to it b\- its centre, and projects on either 



than this flatlN'-expanded, toothci. radiating peltate 

 hair, when seen under the microscojie. 



Other plants show different peltate forms, such as 

 the Sea Bucktliorn. the paleae of many young ferns, 

 the Wallflower and many other cruciferous plants, 

 Cornel, and so on. Figure 5 illustrates one taken 

 from tile leaf of Wild Cornel, and this is exactly' the 

 same in form as a similar hair from the Wallflower 

 leaf. It is curious to note how masses of these low- 

 growing, expanded flat hairs deck the leaf-surface, 

 all more or less of the same size and height, 

 the splayed tijis almost ptiking into each other. 



V. — iiri Jointed [h) Clup.i;ed Plant Hairs. 

 J(,)inted hairs, compared with other forms on 

 the whole, are by no means so common, \ct 

 the\- are met with in considerable numbers, and 

 may be very well seen on the leaves of Hedge 

 Woundwort and many of its allies in the large 

 Natural Order, Labiatae : in Common Fleabane, 

 Bugle, Mossy Saxifrage, Foxglove, Germander 

 Speedwell, on the plants from whence the 

 accomjianying illustrations have been taken, and 

 on the loose, hairy tissue on the surface of the 

 stigma in many of the Orchidaceae. 



If a hair of this kind be examined it will be 

 foimd to show, at certain marked distances up its 



length, peculiar swollen 



joints that l(_)ok \-ery 



much like a series of 



knuckles, which seem 



to lit into sockets, the 



side 



a horizontal wa\-, thus forming a kind of 



shield or very flattened plate, which is membranous 

 in texture, built up of man\- cells, and either more or 

 less smooth and even round its margin, or cut up into 

 numbers of sharp, delicate teeth of man\- varying 

 lengths. It is owing to the presence of these 

 " plates " that man\- plants present a scaly, scurf}- 

 surface. One need but look at Figure 6, a hair taken 

 from the leaf surface of Blcafiiiiis. to understand the 

 reason for the leaf's lepidote appearance, nor can 

 one well wish to see anything more rich in form 



Figure 6. 



tiGURE 3. 



Peltate Hair from tlie under siir- 

 Hair from tlie leaf of Cornel. j^ce of the loaf of Ehaf^iiiis. 



latter being much more clearly noticed in some 

 instances than in others. The Purple Dead -nettle 

 (see Figure 8) shows interesting examples of good 

 jointed hair structures, which are extremeh- sharp- 

 pointed. Those on the stem of one of the common 

 garden species of Harpaliuni (see Figure 9) are really 

 (juaint-looking little things with their thickened 

 joints. cur\'ed. sharp tips, and remarkabh' rough 

 surfaces : indeed, imagination can almost liken them 

 to the claws of a crab ! Figure 10, representing a 

 hair from the stem of the Mouse-ear Chickvveed, is 

 one the prettiest of all. perhaps, for there is a 

 slenderness about it that is graceful, and the way in 

 which joint fits joint is beautiful. In the Pineapple 

 Sage (see Figure 7) are some glandular hairs, on the 

 \'eins of the leaves, and the pedicels of these are 

 distinctly pointed. When touched firmly, this plant 

 emits a delicious odour of pineapple (which probably 



