48 The Nature and Origin of Stipules. 



Galium Aparine L., in common with the six-leaved species, the 

 earlier whorls are of four leaves only, representing the ancestral 

 condition. In Rubia tinctorium L., the opposite leaves of the 

 subterranean portion of the stem are exstipulate. At the first 

 aerial node there is a whorl of four, interpetiolar stipules being 

 present, and in the higher whorls there are six leaves.* This is 

 a series of long range, though lacking in intermediate steps. 



Another case in which there is present a nodal girdle from 

 which the stipular bundles arise is that of Humulus Lupulus (fig. 

 80), but there are three bundles in each leaf-trace. They are 

 placed at about equal distances around the circumference of the 

 stem, and the girdle-bundles proper occupy only about one-third 

 of the periphery on each side. From them a part of the stipular 

 bundles arise, the remainder originating directly from the lateral 

 bundles of the leaf-traces. 



It would be to small purpose that examples should be further 

 multiplied. From those already cited we may confidently deduce 

 the following conclusions : 



1. The sheathing petiole has its origin independently of the true 

 petiole and is formed by a concomitant development of the lateral 

 and central-basal portions of the primitive leaf. 



2. The ligule is a special development of the apical parts of the 

 lateral portions of the primitive leaf along the ridge between the 

 sheathing petiole and the distal parts of the leaf. It may be sup- 

 plied with veins either by the marginal bundles of the sheath or 

 by tangential branches from those entering the blade. The 

 sheathing petiole may disappear by degeneration, rendering the 

 ligule axillary as in many species of Potamogeton. 



3. The ochrea is related to the ligule and is generally associated 

 with the sheathing petiole. It consists of the apical tissues de- 

 veloped in those cases where the sheathing petiole completely sur- 

 rounds the stem or did so in the ancestral condition. The part 

 of the ochrea posterior to the lamina or petiole may be called its 

 ligular portion and is usually supplied by bundles arising tan- 

 gentially from the main ones. 



4. The lateral portions of the primitive leaf, when separated in 

 greater or less degree, constitute stipules in the usual acceptation 

 of the term. They are variously modified by subsequent evolu- 



*Sir John Lubbock. Jour. Lin. Soc. Loud. 30 : 504. 1894. 



