650 MINNESOTA BOTANICAL STUDIES. 



As the embryo departs from its primitive spherical form it is 

 evident that its axis lies more or less directly across the ovular 

 cavity. As the plumule develops superficially near one side of 

 this flat expanse of tissue the remaining larger surface is to be 

 considered as that of the young cotyledon. The cotyledon 

 soon meets obstruction to its further growth in the horizontal 

 plane and hence turns down into the ovular cavity. Its later 

 bifurcation is undoubtedly the result of its having to adjust it- 

 self to the cylindrical cavity in which it grows. That the 

 shape of the cavity does to some extent affect the shape of the 

 cotyledon seems to be evidenced by the fact that the cotyledon- 

 ary lobes are at all times closely appressed to their enclosing in- 

 vestments. The bifurcation extends along aline of mechanical 

 stress. 



The mature embryo of Nelumbo can perhaps best be com- 

 pared with those of the grasses, especially one having but a 

 small amount of cotyledonary tissue below the junction of the 

 plumule and cotyledon. The embryo of the wild rice, Ztzania 

 aquattca, as figured by Kennedy ('99, pi. J. Jig. 2224) af- 

 fords such an example. It has a long epicotyl and a very 

 short hypocotyl which is imbedded in a small amount of coty- 

 ledonary tissue. The cotyledon grows around and nearly en- 

 closes the plumule with a uniform thickness of tissue. In 

 Nelumbo the conditions are almost exactly similar, except that 

 the cotyledon in addition to growing around the plumule has 

 become divided lengthwise nearly to the base into two equal 

 parts. 



THE SYSTEMATIC POSITION OF THE NYMPH^EACE^E. 



As indicated above the one character which has led to the 

 placing of the Nymphagaceae among the Dictotyledons is the 

 structure of the embryo in the seed. In their other characters 

 they conform more nearly to the Monocotyledons. The embryo 

 of Nelumbo has been shown to be monocotyledonous in its de- 

 velopment. Although in the other genera there is present in 

 the seed a functional endosperm and perisperm, a careful ex- 

 amination of the mature embryos shows them to be in all essen- 

 tial respects quite similar to that of Nelumbo. Those common 

 characters, then, which have previously united these plants into 

 a family justify the conclusion that they agree in embryogeny. 

 In order to remove all possible doubt the embryogeny of a 



