The Nature and Origin of Stipules. 25 



adapted for specialization in this direction, it was the one upon 

 which the office devolved. Eveiy botanist knows what an endless 

 variety of forms and special adaptations of particular foliar 

 parts have arisen in the course of evolution which was inaugu- 

 rated when this setting aside of the leaf to bear in future the 

 weight of the assimilative function took place, or rather when this 

 additional function was placed upon it, for the old protective 

 function has always been retained, though it has become less no- 

 ticeable as the new function has overshadowed the old. 



There has been in the line of vegetable descent a progressive 

 development of the foliar organ, and a history of this devel- 

 opment, together with that of other organs, if it were obtainable, 

 would give us a complete phylogeny of the flowering plants, and 

 leave no morphological problem unsolved,* but as the geological 

 record is very incomplete, and we have in the lower Cretaceous 

 an already well developed and much differentiated angiospermous 

 flora of the earlier history of which almost nothing is known, we 

 must seek other sources of information in determining the homol- 

 ogies of parts. At this juncture we may safely follow the exam- 

 ple of the zoologists and turn to embryology for the evidence 

 which geology, as yet, refuses to give except in fragments 

 Among animals, as the phylogeny and ontogeny are found to par- 

 allel one another, so we may feel confident they will be found to 

 do among plants when the geological record shall be more com- 

 pletely unearthed. 



It has become a well established part of the theory of evolu- 

 tion that each individual organism epitomizes more or less fully 

 in its development the historical steps in the evolution of the 

 type to which it belongs. f By the application of this law of re- 



* "On this same view of descent with modification most of the facts in mor- 

 phology become intelligible, whether we look to the same pattern displayed by 

 the different species of the same class in their homologous organs, to whatever 

 purpose applied, or to the serial and lateral homologies in each individual ani- 

 mal and plant." Charles Darwin, Origin of Species, 1859. Am. Ed. 6, 2. 

 264. 1889. See also p. 239, el seq. 



f This theory, known as Von Baer's law, was promulgated by that scientist 

 in his Ueber Entwicklungsgeschichte der Thiere, 224. 1828-37. 



See also F. M. Balfour. Comparative Embryology. Ed. 2, 1: 2. 1885. 



Opposed to this law is Adam Sedgewick. On the Law of Development 

 commonly known as Von Baer's Law. Quar. Jour. Mic. Soc. (II), 36: 35. 

 1894. 



