EXOGENOUS STRUCTURE 



287 



ogens: Prepare thin cross-sections of the stems of meni- 

 spermum (moonseed), one year old, of geranium or of tomato 

 plant. Other greenhouse or garden 

 plants may be employed. Stain with 

 hematoxylin. Make a permanent 

 mount. Study with low power, and 

 make a sketch showing the shape and 

 location of the fibro-vascular bundles. 

 (Fig. 455.) Save the mount for 

 further study. If menispermum stems 

 are not easily obtained, ivy (Hedera 

 helix), clematis, geranium, coleus, 

 tomato or other plants may be substi- 

 tuted. In woody stems the compres- 

 sion is such that the student is usu- 



455. Arrangement of tissues in 

 2-yenr-old stem of moonseed. 

 /), pith; /, fundamental tis- 

 sue; e, epidermis. The fibro- 



vascuiar bundles are very ally puzzled to understand the bundle 



The 



prominent. 



structure. The subject will be sim- 

 plified if he compares (on cross-section) the bundles in such 

 a plant as the cucumber with that part of the vascular ring 

 that lies between any two medullary rays in one-year-old 

 stems of peach, 

 elm, oak. 



488. Other 

 Stems. — Be- 

 sides the two 

 types of stems 

 studied above, 

 which are prev- 

 alent among 

 phenogams, 

 there are other 

 kinds of struc- 

 tures of stems 



among the Cryp- 456. Cross-section of root of brake (Pteris aquilina), showing 

 tno-Qm • A nnm twelve concentric fibro-vascuhir bundles. The two long 



UU^dlllh. A tom- dark 8tranc]8 are composed of fibrous tissue. 



