342 EXPLANATION OF THE PLATES. 



are 3, 4, or 5-parted : as in the figures, c. c. c. They occupy 

 the situation, apparently of the medulla, but can scarcely be 

 considered as cellular processes. 



Fig. 3. A transverse slice of the petiole of Canna indica (mode- 

 rately magnified), in which the vessels are arranged in dis- 

 tinct fasciculi, nearly of the same size in the centre of the 

 section ; alternately larger and smaller (a. b. a. b.) near the 

 circumference on the convex surface, or that part of the peti- 

 ole which is towards the under side of the leaf ; and all small 

 (c. c. c. c. c. c.) on the concave surface, d. d. d. Pneumatic 

 or air-cells, continued also into the mid-rib. 



Fig. 4. — A portion of the foliar expansion of the Canna magnifi- 

 ed, in which it will be seen that the costs or ribbed lines 

 e. e. e. are continuations of those on the concave surface of 

 the midrib, curved outwards in opposite pairs, between the 

 basis and point of the leaf; but the central fasciculi pass 

 along to the apex. All the lateral vessels do not go off from 

 the midrib (b. b.), but some of them are as at a. a. branches 

 of others. At the margins they all inosculate. 



Fig. 5. — A diagram illustrating the origin and connexion of 

 branches. The figure may be imagined as a tree 4 years old. 

 The cone a. representing the first year's growth ; b. b. The 

 second ; c. c. The third, and d. d. The fourth. The buds 

 furnishing the branches e.f. g. h. are all generated in the 

 surface of a. in the spring of the first year ; but on that year 

 e. only sprouts into a branch ; on the surface of which is 

 generated i, which in its turn generates k. In this series, each 

 branch has sprung in regular succession from that of the 

 former year ; the age of the branch being marked by the 

 number of ligneous layers : thus k, which is one year old, is 

 covered with one ligneous layer ; i. with two, and e. with 

 three ; while the original trunk has four, which give the age 

 of the germ whence e. originated. But g. has two layers, 

 only, and/, h. no more than one, although shooting from the 

 same surface as e. which is thus explained. The branch g. 

 sprung from an adventitious bud, which protruded in the 

 second year of the growth of the stem ; and, therefore, al- 

 though the germ whence it originated is as old as that of e. 

 yet it is covered with 2 ligneous layers only ; and the branch 

 /. which it has protruded in regular succession, has but one, or 

 is no older than k., the third in succession on e. In the same 

 manner the branches f. and h, which have also sprung from 

 adventitious buds, are of the same age as k, although their 

 germs were generated on d. and are consequently coeval 

 with the first developement of the trunk. 



