5 TIPULES. 51 



of the mature adult leaves. We cannot take for this purpose the 

 plumule, the bud of the seed, for it is a very special kind of bud and 

 it does not therefore show, in its development in the leaves of the seed- 

 ling, an historical series such as is found in the ordinary bud, espec- 

 ially if it be a subterranean one. 



The first leaves of a young shoot of false indigo as it springs from 

 a strong subterranean bud are mere sheathing scales, representing 

 the primitive leaf-forms of some very remote ancestor, then follow 

 one or two which are three-toothed at the apex and another in which 

 the central tooth has developed into a small blade. Next the blade 

 shows the three leaflets typical of the adult leaf and the clefts separat- 

 ing the lateral teeth of the scale have deepened. These teeth are in 

 fact the tips of adnate stipules. The farther up the stem we carry our 

 observations the greater the. degree of separation of the stipules and 

 the greater the relative development of the lamina with its petiole 

 which has appeared first at about the seventh leaf. As soon as the 

 separation of the stipules is complete, at about the tenth leaf, degen- 

 eration begins, and only a few leaves higher up scarcely any trace of 

 them can be found. The interpretation of these facts shows us that 

 the leaves of the primitive ancestral flowering plants were mere pro- 

 tective scales, that in the course of evolution the need of greater as- 

 similative capacity arose and as the leaf was best adapted for receiv- 

 ing this special function it was upon it that the office devolved. Then 

 began that series of evolutionary changes which has formed out of 

 the same primitive scale all the great variety of leaf -forms which to- 

 day meet us on every hand and please our eyes, our tastes and fancies 

 with never ceasing changes, just as the potter with one lump of clay 

 may make a hundred different objects of usefulness and beauty. That 

 this is the correct interpretation is more firmly established by the fact 

 that the farther back we go in the records of the past and study the 

 forms of fossil leaves, the more simple they become, and though they 

 have not yet been traced back to the most primitive forms, since 

 authentic remains of the primitive flowering plants have not yet been 

 found, yet all the evidence we have from this source points in the di- 

 rection of our conclusion. 



We have seen that in the false indigo it was the tip of the scale 

 which developed into the leaf -blade bearing the assimilative function 

 and that the lateral parts became first adnate stipules, then free sti- 

 pules and later disappeared by degeneration. But, is this always the 

 case ? It is not, and we are now brought to the third question: How 

 is it that some families of plants have no stipules at all, except per- 

 haps in a few species, and in others they are wanting in few species 

 if any ? The answer is that it is owing merely to the different ways 



