172 



BOTANY. 



The steins may be modified into thorns for protection, as we 

 see in many trees and shrubs, and parts of leaves may be simi- 

 larly changed, as in the thistle. The underground steins often 

 become much changed, forming bulbs, tubers, root stocks, etc. 



FIG. 93. A, base of a plant of shepherd 's-purse (Capsellabursa-pastoris), 

 x %. r, the main root. B, upper part of the inflorescence, x 1. C, two 

 leaves: i, from the upper part; n, from the base of the plant, x 1. D, a 

 flower, x 3. E, the same, with sepals and petals removed, x 3. F, petal. G, 

 sepal. H, stamen, x 10. /, filament, an. anther. /, a fruit with one of the 

 valves removed to show the seeds, x 4. J, longitudinal section of a seed, 

 x 8. K, the embryo removed from the seed, x 8. I, the first leaves (coty- 

 ledons), st. the stem ending in the root. L, cross-section of the stem, x 20. 

 /&. fibro-vascular bundle. M, a similar section of the main root, x 15. N, 

 diagram of the flower. 



much as in the monocotyledons. These structures are espe- 

 cially found in plants which die down to the ground each year, 

 and contain supplies of nourishment for the rapid growth of 

 the annual shoots. 



The structure of the tissues, and the peculiarities of the 

 flower and fruit, will be better understood by a somewhat care- 



