CHAPTER IV. PLANT-HAIRS OR TRICHOMES. 41 



base, margin, surface and texture of the leaflets, using the descriptive language 

 of botany : Those of the Pea, the Hemp, Sweet Clover, Common Field-Clover, 

 Meadow-Rue, Locust, Honey Locust, and Ash. 



5. Describe the Phyllotaxy of the Locust, of the Sycamore, of the Crab- 

 Apple, of the Common Milk-Weed, of the Elm, of the Canada Lily, of the 

 Flax, and of the White Pine. 



6. Examine the buds or unfolding leaves of the following plants and 

 determine the vernation : The Hickory, the Custard Apple, the Sweet Flag, 

 the House Geranium, the Oak, the Sycamore, the Plantain, the Maple, the 

 Common Polypody and the Ash. 



CHAPTER IV.— PLANT-HAIRS OR TRICHOMES. 



Though these organs are, for the most part, minute and simple 

 in their structure, we are justified, on account of the important 

 functions which many of them perform, in classing them as dis- 

 tinct organs of vegetation. They are, for the most part, appen- 

 dages to the epidermis ; sometimes, however, they include tissues 

 of the hypoderma, and rarely, as in the glandular hairs of the 

 Sundew, they are quite complex structures, and contain vascular 

 tissues. They may be borne by any other organ of the plant, 

 that is, by root, stem or leaves, and they usually occur without 

 definite order. In rare instances, organs which we must regard 

 as hairs, occur in interior tissues, particularly in some aquatic 

 plants, like the Water-lilies, that have large inter-cellular spaces 

 or air channels in their stems and leaves. In such cases they 

 are located in the tissues adjacent to the inter-cellular spaces, 

 and project into the latter as other hairs do into the open air. 

 These internal hairs are called trichoblasts. (See Vegetable 

 Histology). 



The primary function of hairs appears to be that of absorb- 

 ing nourishment. How important root hairs are in this respect 

 has already been stated, but they are not the only ones that per- 

 form this function. The uses of the glandular hairs of Sundew 

 and other insectivorous plants have just been mentioned, but it 

 is also known that the hairs on the stems and leaves of the 

 Chinese Primrose, the House Geranium (Fig. 155), and some 

 species of Saxifrage, are active agents in absorbing nitrogenous 

 compounds from the air, and there is good reason to believe 

 that in many other plants they perform similar important serv- 

 ices. 



