A LESSON ON BUTTERCUPS. 



213 



The root will be found to be in general only moderately 

 developed. Its function is chiefly that of fixation, and 

 root hairs are scarce because the other submerged parts 

 share in absorption. The stem is smooth, almost cylin- 

 drical, hollow, solid at the nodes. Short rootlets are given 

 off at the nodes. Leaves arise here and in their axils occur 

 branches which repeat the structure of the stem. Portions 

 broken off are capable of rooting and growing fresh plants. 



If the stem is sectioned it will be 

 found that the inside tissue (paren- 

 chyma) is loosely arranged, having large 

 intercellular spaces. A ring of vas- 

 cular bundles is present, but the woody 

 vessels are few. No stomata are pre- 

 sent. The whole stem lacks the robust 

 character of the terrestrial type, and 

 out of water it cannot stand erect. In 

 the water it is of course buoyed up. 

 From the water all the necessaiy 

 mineral salts, carbon dioxide and oxy- 

 gen are obtained direct, hence the re- 

 duced nature of the wood vessels and 

 the absence of stomata. 



In plants growing in swiftly running 

 streams the leaves are all more or less 

 submerged. The leaf sheath is large 

 and membranous, enveloping the young 

 buds ; in most cases the leaf stalk is 

 undeveloped or only slightly so. The 

 blade is very much divided up dis- 

 sected type being reduced to a bundle of filaments. 

 These filaments have an abundance of green corpuscles 

 (chloroplasts) in the epidermis, as may be seen in section. 

 Also the conducting vessels are quite rudimentary. There 

 are no stomata. G-ases and mineral salts pass into the 

 plant by absorption. 



It is quite apparent that the clearly defined differentia- 

 tion of functions of the organs root, stem, and leaves is 

 largely obliterated in the water buttercup. The form of 

 these persists but the functions are generalised, stem and 



Fig. 81. The Water 

 Crowfoot, showing 

 floating and sub- 

 merged types of 

 leaf. 



