THE MOOTS OF PLANTS. 165 



Ivy (Hedera), Poison Ivy {Rhus), the Virgiuia Creeper {Am- 

 pelopsis), etc. 



213. — In form roots are generally fibrous, and this is 

 manifestly their best form, in so far as they are organs for 

 obtaining dissolved matters from the soil. In perennials, 

 however, as the stems become larger the roots increase cor- 

 respondingly to support the additional weight ; they thus 

 become hold-fasts or mechanical supports. In other cases 

 they are made the recipients of assimilated matters, as starch, 

 sugar, etc., and thus become thickened storehouses. 



In many cases the latter are capable of forming buds and 

 of sending out new stems from the meristem tissue in, or in 

 the vicinity of, the fibro-vascular bundles, as is notably the 

 case in the tuberous root of the sweet potato. 



(a) The root-cap may be studied with the least difficulty in roots 

 which are grown in water. Those of Lemna may be easily obtained, 

 and are excellent. 



(6) Roots of Indian corn. Hyacinth, Impatiens, etc., also furnish 

 easily made and good spefeimens. 



(c) In preparing specimens for examination thin longitudinal sections 

 should be made, and these should be supplemented by transverse sec- 

 tions taken at various heights on a root-tip. 



(ri!) By the use of staining fluids, as carmine, magenta, etc., some 

 points in the structure will be made more evident. Iodine should also 

 be used ; by treatment with it, the starch which is present in the root, 

 tip in many, if not all, cases may be seen. 



(«) For studying the formation and development of new roots suc- 

 culent plants should be chosen, as the sections of their tissues are more 

 transparent than those of other plants. On this account many water 

 plants are to be preferred. Among land plants, Impatiens is one of 

 the best; it always has a large number of forming roots on its stem 

 near or at the surface of the ground. 



(f) Vertical sections of the papillae, showing the point of appearance 

 of new roots, should be made. If many longitudinal slices of the 

 lower part of the stem of Impatiens are made in a section-cutter, it will 

 almost certainly happen that some good specimens will be found. 



