THE HAIKS OF PLANTS. 



Bound, on their immersion in -water. They are found in the common mustard (Sinapis], 

 which any one may examine after immersion for three hours, and hare the form of an 

 elongated cell, terminated by a bell-shaped expansion. In the seed-covering of the 

 Collomia grandiflora and common sage (Salvid), each hair is simply an elongated cell of 

 even diameter, terminated by a rounded obtuse end, and with a single coiled elastic 

 fibre proceeding from the base to the apex. This is an interesting object, but requires 

 considerable dexterity and quickness to see it with advantage. Slice the smallest portion 

 of the outside of the common sage, and place it dry between two glasses tinder the micro- 

 scope. No hairs will then be perceived ; but if, whilst it is so placed, and the eye is upon 

 it, a drop of water be insinuated between the glasses, until it touch the seed, there will 

 instantly start out scores of long fibro-cellular hairs ; and as the complete development 

 occupies a perceptible interval of time, the eye may readily trace the process of elonga- 

 tion. "When the change has been entirely effected, the object has no longer a defined 

 smooth border, but is bounded all round by thread-like projecting points. A similar 

 structure has been discovered in the hairs of the seed of Acanthodium, but with this 

 difference, that two or three spiral fibres have been traced in one cell ; and in some 

 instances the fibres are broken up into numerous rings. This is doubtless a beautiful 

 object. 



All the foregoing varieties of hairs may be termsd single, but there are others which 

 may fitly be designated as compound. Such are toothed hairs, in which there are short 

 cellular projections on both sides of the hair ; and branched hairs when the teeth are 

 greatly elongated (Fig. 112 rf). In a few instances this development is carried yet fur- 

 ther, and the branches themselves are 

 toothed, and the hair is said to be plumose. 

 In others, the branches are restricted to 

 one side of the hair, when the latter is 

 termed one-sided. 



But perhaps the most interesting cir- 

 cumstance in connexion with the anatomy 

 of hairs, is, that in some plants, as the 

 Sago-palm (Cycas revolutaFig. 114), the 

 cuticle of the hair can be unrolled spirally. 

 Professor Quekett has described this upon 

 the fruit of that plant, and has delineated Fig> nJf^tions of hair from the fruit of the 

 t in Fig. 114. Sago-palm (Cycas revoluta), exhibiting a spiral 



The foregoing remarks have exclusive dis P sition of the membrane, 

 reference to one great division of hairs r/z., the Lymphatic, or such as bear innocuous 

 fluids ; but there is another large division which have a different conformation, and 

 contain juices of highly acrid and poisonous properties. The sting of the nettle (Urtica) 

 is a familiar and painful illustration, but the hairs of the leaves of certain tropical 

 plants are yet better examples. These contain juices so poisonous, that if the hand 

 grasp a leaf, it speedily inflames and swells, and so disturbs the whole system, that life 

 is endangered. Such is the Jatropha when growing in our hot-houses even, and is 

 handled only with the protection of a pair of thick leathern gloves. Moreover, if any 

 part of the body be placed under this tree during a shower of rain, the poison which 

 is washed from the- plant by the water would, in like manner, cause very serious 

 ease. 



The anatomical difference between the lymphatic and secretive variety of hairs is, that 



