224 PRACTICAL BOTANY. 



of E. arvense, treat them with potash, and mount 

 in glycerine : examine them under a high power, and 

 observe 



1. That there is a peripheral band of tissue with 

 dark brown walls : single superficial cells have grown 

 out. as root-hairs. 



2. Then follows a broad band of colourless Cortex, 

 with large intercellular spaces ; this is limited internally 

 by- 



3. A definite layer of cells having the well-marked 

 characteristics of the Bundle-sheath : 



4. Within this is the Phloem-sheath, the cells of 

 which are opposite to those of the bundle-sheath, and 

 are derived with the latter from the inmost layer of the 

 cortex. This surrounds 



5. The vascular cylinder, consisting of 



a. Four Xylem groups, each of which may consist of 

 only one tracheide, while one large element often 

 occupies a central position. 



I. The spaces between these are occupied by ill- 

 defined groups of Phloem, and Conjunctive paren- 

 chyma. 



The arrangement of tissues at the apex of the root of Equisetum 

 may be studied in the same way as above described for the root 

 of Aspidium Filix-Mas, and it will be found to be similar to it 

 in all the more important points. Attention should also be paid 

 to the mode of origin of the lateral roots, which here spring 

 from the phloem-sheath, while in Ferns they arise from cells of 

 the bundle-sheath. 



The Sporangia. 



XI. Examine one of the fertile stems, which rise 

 above ground in the spring, with the naked eye ; ob- 



