208 MORPHOLOGY OF ANGIOSPERMS 



edge in Nuphar lutea. In his recent study of Ceratophyllum 

 Strasburger 84 finds that the embryo in its earlier stages bears 

 a striking resemblance to that of Nelumbo, there being a large 

 spherical mass of cells with no suspensor (Fig. 80). The em- 

 bryo of Nelumbo has the rudiment of a root, although it never 

 develops, the first functional roots coming from the stem above 

 the cotyledon (Fig. 80, s). In Ceratophyllum the reduction 

 due to the water habit has gone further, not even the rudiment 

 of a root appearing in the embryo. The two cotyledons of 

 Ceratophyllum so strongly resemble the condition in Neluinbo, 

 that Strasburger, after examining the embryo of the latter, was 

 forced to believe that here also, as in Ceraiophyllum, there are 

 two cotyledons. 



The occasional occurrence of a whorl of three cotyledons 

 has been reported for Quercus, Amygdalus, Phaseolus, etc., and 

 many other cases are given by Braun. 6 



In this connection, recent suggestions as to the phylogeny 

 of the cotyledon may be referred to. The current opinion re- 

 gards it as a modified foliage leaf, and this is borne out in the 

 majority of Dicotyledons by the assumption of the foliage func- 

 tion. The terminal cotyledon of Monocotyledons, however, 

 seems to belong to a different category, and to hold no relation 

 to a foliage leaf or to a foliar member of any description. In 

 a recent paper H. L. Lyon 88 develops the idea that the cotyle- 

 don of Angiosperms is phylogenetically related to the sucking 

 organ known as the " foot " among Bryophytes and Pterido- 

 phytes. His own summary makes his position clear: 



(1) The typical embryos of the Pteridophytes and Angiosperms 

 differentiate into three primary members, the cotyledon, stem, and 

 root ; (2) cotyledons are not arrested leaves, but are primarily hausto- 

 rial organs originating phylogenetically as the nursing-foot in the 

 Bryophytes and persisting throughout the higher plants ; (3) the mono- 

 cotyledonous condition is the primitive one and prevails in the Bryo- 

 phytes, Pteridophytes, Monocotyledons, and some Gymnpsperms ; the 

 two (sometimes more) cotyledons of the Dicotyledons are jointly the 

 homologue of the single cotyledon of the Monocotyledons ; (4) the 

 cotyledon always occurs at the base of the primary stem ; (5) the hypo- 

 cotyl is a structure peculiar to the Angiosperms, being differentiated 

 between the primary stem and root ; (6) the so-called cotyledon of 

 the Pteridophytes arid Gymnosperms, with the probable exception of 

 Ginkgo and the Cycads, are true foliage leaves. 



