EMBRYOLOGY OF MYOSURUS MINIMUS 



LEROY D. SWINGLE, Ph.D. 

 University of Nebraska 



There is a close superficial resemblance existing be- 

 tween Myosurus and some of the lower forms such as 

 the pines and the Selaginellaceae. For this reason the 

 development of Myosurus presented itself as an inviting 

 field of research. To be sure Bessey (1898) has already 

 given the stages in the development of the pistils. My 

 work in so far as it repeats these early stages serves as a 

 confirmation of his description. 



The developmental stages correspond very closely to 

 those of Ranunculus, which has been investigated by 

 Coulter (1898). The arrangement of the pistils, how- 

 ever, differs from that of Ranunculus in the fact that in 

 Myosurus the receptacle is drawn out into a long central 

 axis around which the pistils are arranged in spiral rows. 

 Acropetal development of the pistils is very marked, so 

 that the axis may lengthen nearly two inches after the 

 pistils at the base have reached maturity (PI. I, Fig. 8). 

 The pistils formed late in the season around the apex 

 of the axis are not pollinated. In respect to this conical 

 arrangement of megasporophylls and the mode of de- 

 velopment of the megasporangia there is at least a super- 

 ficial resemblance to the pines and Selaginella. 



As in most microsporophylls, so here there are four 

 sporangia. At first the stamen is a mass of undiffer- 

 entiated meristem (PL I, Fig. 1), but soon the limits of 

 the sporangia become visible. The meristem cells within 

 the areas which are to become sporangia begin to de- 

 generate, while the first hypodermal layer becomes active 

 in division. The cells, archesporial in character, divide 

 periclinally to produce an outer primary wall cell and an 

 inner primary tapetal cell. The former cell divides once 



