68 



ESSENTIALS OF VEGETABLE PHARMACOGNOSY. 



of blades, as at a, but as transverse sec- 

 tions of them, as at c. If tbe ray consists 

 of but one row of cells in ^'idth, then ?5neh 

 a row will be exhibited upon the tangen- 

 tial section, its vertical height varying 

 from a very few to quite a large number 

 of cells. If, upon the other hand, it pos- 

 sess a lateral breadth of several thick- 

 nesses of cells, of 5 in our figure, this 



condition will exist only at its middle por- 

 tions. At its upper and lower limits it will 

 always be reduced to the thickness of a usually definite for the species, of vascu- 



of bundles the latter are found more or 

 less scattered through the fundamental 

 or medullary tissue, though there is com- 

 monly more or less of a concentration of 

 them in some one region, usually toward 

 the periphery of the stele. The endo- 

 dermis of such plants is commonly known 

 as a Nucleus Sheath. 



Finally, we note that in many plants, 

 represented among drugs by the ferns, 

 the stele, as the stem, possesses a number, 



single cell, so that the tangential aspect 

 of a medullary ray is almost always that 

 of an ellipse, broad or narrow, according 

 to the number of rows of cells of which 

 it consists, in contrast with the extent of 

 its upward and downward extension. 



The pith or medulla in some stems after 

 a time disappears more or less completely, 

 leaving a cylindrical hollow cavity. This 

 may be coutinnous through the nodes or 



separated at those poluts by transverse 

 partitions. 



In monocotyledons we have the Con- 

 centric Bundle, in which the one element 

 surrounds and encloses the other. In all 

 medicinal stems possessing concentric 

 bundles, except tbe male fern, it is the 

 xylem which encloses tbe phloem. If 

 the two cylinders thus formed have not a 

 common centre, the bundle is designated 

 as Closed Collateral, and this is far more 

 common than the typically concentric 

 form. It is clear that in tbe last two 



lar bundles, each invested by its own en- 

 dodermis. In such plants no epidermis is 

 developed, tbe hypoderm, developed from 

 the periblem, being superficial. 



VERTICAL ANO LATERAL EXTENSION OF THE 



STEM, AND OUTGROWTHS FROM IT. 



Examining a radial section of the tip of 

 the stem we find, in addition to the struc- 

 tures already considered as belonging pri- 

 marily to itself, protuberances, consisting 

 of masses of meristem tissue belonging to 

 the periblem and the dermatogen. 

 Shortly each of these tissue masses as- 

 sumes the condition of tbe primary grow- 

 ing point of the main stem. It may de- 

 velop into a leaf, the structure of which 

 will be considered further on, or a branch, 



t I 9 



which latter process is a mere repetition 

 of that already considered in relation to 

 the primary stem. In either case The 

 vascular bundles exhibit a connection, 

 variable in its details, with those of the 

 stem from which it develops. The nor- 

 mal method is for a branch and leaf to 



forms a cambium cylinder, such as dis- develop together, the former in the axil 



tinguishes the stele, possessing the form 

 previously considered, cannot be formed. 

 In such plants indefinite growth in thick- 

 ness of the bundles obviously cannot oc- 



of the latter, as already recorded. If two 

 or more leaves, with their branches, de- 

 velop at the same node, it results in the 

 opposite or verticillate arrangement. If 



cur and the same is true of the entire but one, then, of those developing at dif- 



stele, unless new bundles may develop in 

 it. Usually this does not occur, but if the 

 upper portion of the plant shall branch 

 and continue to extend its leafy surface, 

 meristem tissue will then form toward 



the outer portion of the stele, and from study of the leaf. 



ferent levels, each is successively sepa- 

 rated from the former by a uniform por- 

 tion of the stem circumference, so that a 

 spiral arrangement results. This spiral 

 will be considered when we come to the 



this new bundles will successively arise, 

 so that the thickness of the trunk will 

 keep pace with the extension of the 

 crown, notwithstanding that the individ- 

 ual bundles do not increase in thickness 

 after the completion of their primary 

 structure. In stems possessing this form 



The point at which one or more leaves 

 develop hag already been defined as the 

 node, and the portion of stem inter- 

 vening between two nodes as the inter- 

 node. At first the internodes are so short 

 as to be scarcely perceptible, but they 

 continue to grow until a length more oi 



