1914I BAILEY & SINNOTT—PHYLOGENY OF ANGIOSPERMS 37 



the dicotyledons. With the advent of a severe winter season and 

 the consequent acquirement of the deciduous habit in connection 

 with the leaves, the organization of these storage systems about the 

 leaf traces as permanent centers was no longer advantageous or 

 desirable. Thus in the development of the "multiseriate" type 

 of ray which characterizes the majority of living dicotyledons, the 

 enlarged units of the aggregating mass of foliar ray tissue have been 

 diffused more or less uniformly throughout the stem. Besides 

 being less unwieldy, this system of smaller rays affords equally large 

 capacity for storage and a more convenient general relation between 

 conducting, supporting, and storage tissue. 



The principal arguments in favor of this hypothesis were first 

 formulated in a paper presented by Jeffrey ('09) before the 

 ^ tanical Society of America at Baltimore. 



?■ One of the most striking triumphs of modern plant anatomy is to have 



^covered man^T examples of recapitulationary confirmation of the principle 



1 evolution. Tfl take a modern and striking example, let us consider our 



common and flourishing northern genus, the oak. You are all familiar with 



cry broad rays which constitute so ornamental a feature of the structure 



- * 



01 oak wood. You are likewise doubtless aware that the weight of paleo- 

 botanical evidence speaks for the derivation of the oaks from ancestors resem- 

 bling the chestnuts, since the older oaks approach the chestnuts both in their 

 ioliage and in their reproductive organs. The wood of the chestnut differs, 

 however, strikingly from that of oaks by the entire absence of large rays. It has 

 been recently discovered that certain oaks of the gold gravels (Miocene- 

 Tertiary) of California have their large rays composed of aggregations of 

 smaller rays. In the seedlings of certain of our existing American oaks this 

 condition, interestingly enough, is a passing phase, which by the loss of the 

 separating fibers in the congeries of small rays produces the characteristic large 



■ 



rays of the adult. This condition of development in the living oaks is all the 

 more significant because in certain breech-fertilized or chalazogamic amentif- 

 erous trees of the present epoch, such as the alder, the hazel, and the horn- 

 beam, such aggregated, so-called false, rays are a permanent feature of structure 

 in the adult. From the anatomical side, in the case of the lower Amentiferae, 

 we have accordingly at the same time an interesting example of the general 

 law of recapitulation and a confirmation of the view expressed by Treub and 

 Nawaschin, on evidence from the gametophytic and reproductive side, that 

 the breech-fertilized Amentiferae are relatively primitive angiosperms. 



The arguments blocked out in this paper have been elaborated 

 under Jeffrey's direction by several students (see bibliography). 



