BOOKS AND CURRENT LITERATURE 



Recent Work on Evolution in the Dicotyledons. — Certain pieces 

 of work emanating from the Phanerogamic Laboratories of Harvard 

 University have thro\vn so much Hght on the evolution of the Dicotyle- 

 dons that they deserve to be made more available to American readers. 

 These studies began with researches on oak wood, but the first con- 

 clusion of wide application was reached by Eames^ when he announced 

 the rather revolutionary view that the primitive Angiosperms were arbo- 

 rescent rather than herbaceous plants, and that their woody cylin- 

 der was a continuous ring of secondary xylem with uniseriate medullar}' 

 rays. Although we naturally do not haVe any of the ancestral Dicoty- 

 ledons at the present time, the genera Casuarina, Alnus and Carpimis 

 probably show as primitive a wood structure as any existing members 

 of the group. Castanea appears to show a simple condition, for its rays 

 are all of the uniseriate type, but it is held- that this is a case of reduc- 

 tion. In the seedlings of white oaks uniseriate rays are exclusively 

 found,' and this seems to be a case of recapitulation, as is indicated by 

 the fact that fossil oaks from the Miocene of California show an inter- 

 mediate condition between uniseriate rays and the broad form which 

 is characteristic of the mature wood of Quercus. These intermediate 

 stages are also to be found in the live oaks and certain of the alders. 

 Moreover Bailey^ has shown that the uniseriate ray may be made to 

 reappear in adult oaks through the influence of a severe wound. In- 

 stances of reversion due to wounding are becoming frequent, and the 

 present case forms an interesting addition to the list. From these dif- 

 ferent lines of evidence the conclusion is dra^ra that the ancestral 

 Dicotyledons had exclusively uniseriate rays, in Avhich respect they 

 resembled Conifers and other living and fossil Gymnosperms. 



' Eames, A. J., On the origin of the herbaceous type in the Angiosperms. Ann. 

 Bot. 25 : 215-224, pis. 14, January 1911. 



^ Bailey, I. W., The evolutionary history of the foliar ray in the wood of the 

 Dicotyledons. Ann. Bot. 26: 647-661, pis. 63-63. July 1912. 



' Eames, A. J., On the origin of the broad ray in Quercus. Bot. Gaz. 49: 161-167, 

 pis. 8-9, March 1910. 



* Bailey, I. W., Reversionary characters of traumatic oak woods. Bot. Gaz. 

 60: 374-380, pis. 11-12, November 1910. 



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