On the Affinities of Ceratophyllacea.. 41 



Remarks on the Structure and Affinities of the Order 

 Ceratophyllacea. By Asa Gray, M. D. 



Read, February 20, 1837. 



The fruit and seed of the genus Ceratophyllum, Linn, were 

 first correctly described and figured by Gaertner,* so long ago 

 as the year 1778 ; a fact worthy of especial notice, since an 

 erroneous view respecting the structure of the seed has been 

 introduced into every subsequent systematic Work that has 

 fallen under my notice, in which an account of that organ is 

 attempted. The only error in the description of Gaertner, is 

 that of considering the proper cotyledons as a separate organ, 

 which (in this as in a few analogous cases) he calls the vitellus ; 

 but it should be borne in mind that the admirable work of this 

 author was prepared at a period when the nature of the embryo 

 was very imperfectly understood. 



L. C. Richardt first pointed out the most remarkable pecu- 

 liarity in the structuie of the embryo, which consists in the 

 presence of four (apparent) cotyledons and a highly developed 

 plumule. Jussieu,J who evidently knew very little of the genus, 

 referred it to the order Naiades ; a very heterogeneous assem- 

 blage as originally constituted, the twelve genera included in 

 it having been since ascertained to belong to at least seven 

 different families. 



* De Fruct. et. Sem. Ptantarum, 1, p. 212, t. 44, fig. 2. 

 t Analyse du Fruit, 1808. 

 t Gen. Plantarum. p. 18. 



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