58 MANUAL OP BOTANY 



form a single foliar body which is placed in the axil of the leaf 

 and is accordingly termed axillary ; and if such stipules cohere 

 by both outer and inner ixiargins so as to form a complete sheath 

 which encircles the stem above the insertion of the leaf {fig. 87, d), 

 as in the Bhubarb, and most other plants of the order Poly- 

 gonacese, they form what is termed an ochrea or intrafoliaceous 

 stipule. 



All the above kinds of stipules occur in plants with alternate 

 leaves, in which such appendages are far more common than 

 in those with opposite leaves. "When the latter plants have 

 stipules these are generally situated in the intervals between 

 the petioles on each side, and are hence termed interpetiolar. 

 In such cases it frequently happens that the opposing stipules 

 of each leaf cohere more or less completely by their outer 

 margins so as to form but one interpetiolar stipule on each 

 side of the stem {fig. 88, s), as is the case in the Cinchonas, 

 the Coffee, and other plants of the natural order Eubiacese to 

 which they belong. 



The stipules are sometimes modified to form spines, much 

 resembling the thorns of the stem, as in Bohimia {fig. 89). 

 In many species of Smilax they take the form of tendrils 

 {fig. 90). 



Stipules, as we have already noticed, are not always present 

 in plants, but their presence or absence in any particular plant 

 is always constant, and although the appearance and arrange- 

 ment of them also vary in different plants, they are always 

 uniform in those of the same species, and even, in some cases, 

 throughout entire natural orders, and thus they frequently 

 supply important distinctive characters in such plants and 

 orders. Thus the plants of the Loganiaoeae are distinguished 

 from those of the allied order Apocynaceae by possessing inter- 

 petiolar stipules ; and the plants of the Polygonacess usually 

 from those of allied orders by intrafoliaceous stipules, or 

 ochreEe. 



Stipules are very rare in Monocotyledons ; among the Cryp- 

 togams they are only present in the Marattiaceee, a group of 

 the Ferns. 



The Mesopodium or Petiole. — According to the presence or 

 absence of this portion of the leaf-axis, leaves are said to be 

 stalked or sessile. When the petiole is present it is as a rule 

 more or less cylindrical, but frequently is almost semicircular 

 in section, the upper surface being flattened and sometimes 

 grooved. It may'be very short or considerably elongated. In 



