50 THE PLANT WORLD. 



the pea-vines are climbing up their trellises of brush, we shall see 

 stipules of quite another sort. Down at the base of the petiole, as 

 before, they will be found, but broadly expanded, as large as the leaf- 

 lets and like them green and succulent. These stipules do not fall 

 away but form part of the laboratory of the plant where in the sun- 

 light starch is constantly forming in the abundant chlorophyl grains 

 for the use of the plant in building its tissues, forming its flowers and 

 ripening its seed. 



Another case of great interest in which the stipules serve the 

 same purpose as the leaf-blade is found in the bedstraws and their 

 relatives, which are described as having whorled leaves but are recog- 

 nized in reality to have opposite leaves, the remaining parts of the 

 whorl being stipules which have attained the same size and import- 

 ance as the leaves themselves but never producing buds in their axils, 

 the branches all springing from the axils of the opposite true leaves, 

 as any one may observe. Nor is the vascular tissue supplied directly 

 from the stem bundles as to the true leaves, but from a nodal girdle 

 which originates in the bundles belonging to the leaves. We have 

 already spoken of the protective function of the spiny stipules of the 

 locust and how they ward off intruders. Similar spines in the Acacias, 

 a genus of tropical leguminous plants, have in some species attained 

 a very remarkable size, presenting the appearance of a pair of minia- 

 ture ox-horns at the base of each leaf. These are hollow, and we are 

 told by the naturalist. Belt, in his narrative of travels in Nicaragua 

 that some kinds of ants often take possession and find in them safe 

 and comfortable homes. These are the most important of the uses of 

 stipules. 



Next we are asked: Why did stipules come to be ? This is a more 

 difficult question and requires us to go farther for an answer. We 

 must examine the growth of buds and compare with one another the 

 simple outer scales, the mature leaves in all their parts, and the grad- 

 ually modified intermediate forms of the lower part of a young shoot. 

 Still further we must go to the records of the dead past preserved in 

 the rocks and compare the forms of fossil leaves with those of their 

 most nearly related living representatives and examine the data ob- 

 tained in the light of the established theories of creation by evolution, 

 of the more or less complete summing up in the development of each 

 organic individual of the historic steps in the evolution of its type, 

 and the gradual disappearance of ancestral organs that have become 

 useless. As we observe in order the leaves of the young stem of such 

 plants as the false indigo or agrimony, whose subterranean buds 

 develop in spring-time under very primitive conditions, we find a 

 series of forms representing a summary of the historical development 



