80 



ESSENTIALS OF VEGETABLE PHARMACOGNOSY. 



petiole the surfaces may become laterally 

 placed, the edges vertical. In a few leaves 

 the surfaces are normally in the latter 

 position. Between the dorsal and ven- 

 tral surfaces there are usually differences 

 sufficient to necessitate their description 

 separately. In such descriptions it is bet- 

 ter to speak of the dorsal surface as be- 

 ing underneath rather than **below," as 

 the latter term may confuse it with the 

 basal region. The connection of the leaf 

 with the stem is usually by its base, con- 

 sisting of a pulvinus and forming an ar- 

 ticulation, the structure of which is de- 

 signed to afford a prompt and ready sep- 

 aration of the leaf at the conclusion of 

 the performance of its function, as well 

 as to provide for certain movements and 

 changes of position during life. In this 

 case the stipule is often present as a 

 prominent organ and of exceptional value 

 and importance in classification and di- 

 agnosis, as in such families as Rubiaceae, 

 Salicaceae and Violaceae. It is to be 

 studied as to duration, falling sometimes 

 before the expansion of the leaf, or per- 

 sisting to various degrees after this pe- 

 riod, and as to the scar which it leaves, 

 as to its freedom from or degree of adna- 

 tion to the leaf, the stem or to the adja- 

 cent stipule in case of opposite leaves. In 

 the latter case the organ formed by the 

 union of two stipules belonging to oppo- 

 site leaves is designated an In^^-apetiolar 

 stipule (Fig. 3S9a). Especial importance 

 attaches to the characters of these, as 

 they frequently develop into remarkably 

 formed and appendaged bodies, as es- 

 pecially in the Rubiaceae, a most impor- 

 tant medicinal family. Cases even oc- 

 cur in which the two stipules of a single 

 leaf become contiguous and connate. The 

 stipule is, moreover, to be studied in 

 every detail in which the leaf is to be 

 studied in connection with the classifica- 

 tions which follow. Leaves which do not 

 possess stipules are called Exstipulate; 

 those which do, Stipulate. Stipulate 

 leaves are very frequently mistaken for 

 exstipulate when the stipules are cadu- 

 cous or fugacious. It is frequently the 

 stipules which are modified to form the 

 scales of scaly buds. 



At other times the connection of the leaf 

 to the stem is by means of the adnation 



of more or less of its petiole, or even of 

 its blade thereto, producing in the former 

 case a ridge, in the latter a pair of herba- 

 ceous wings upon the stem (Fig. 395), In 

 this case perfect articulation does not oc- 

 and 



cur, ana stipule characters 

 wanting or greatly modified. 



are either 



F.g.38T 



^•g »»?. 



The petiole instead of being adnate may 

 be wanting, or it may be very short. In 

 this case the relative position of the base 

 of the blade to the stem will depend upon 

 its form. 



The attachment of the petiole to the 

 blade is always really marginal, though 

 by the cohesion of basal lobes (Fig. 390) 

 it is often apparently intra-marginal or 

 even central. Basal lobes may, upon the 

 other hand, be adnate along the petiole, 

 or the same appearance may be produced 

 by the gradual differentiation of petiole 

 into blade. When the margins of the 

 petiole throughout are herbaceous and in 

 continuation with the blade, the petiole 

 is said to be Margined or Winged. In 

 the blade of the leaf the cortex and epi- 

 dermis bordering each branch system of 

 a rib and its veins may be entirely con- 

 tinuous with that of the adjacent one 

 upon either side, so that the blade will be 

 entirely unsegmented, and its margin en- 



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