-Ian., 190'^.] Chtytonia virginica. 549 



THE DEVELOPMENT OF THE EMBRYO-SAC AND 

 EMBRYO OF CLAYTONIA VIRGINICA.- 



Mklvit^le Thukston Cook. 



Claytonia virginica Linn. wa.s selected a,s a type for class study. 

 The number of interesting points led me to complete the .series of 

 preparations and prepare the results for publication. The wide 

 distribution and the ease with which the material can be killed 

 and prepared for class work may make it an equally desirable 

 type for others who may wish to study a dicotyl with unequally 

 developed cotyledons. 



METHODS. 



The material was killed and fixed in Fleming's solution, pa.ssed 

 thrcnigh the alcohols, iml-edded in paraffin and cut on a Minot 

 microtome. In most cases the sections were cut rather thick. 

 For the very } oung stages only the calyx was removed. The 

 fluid will penetrate the ovules readily until they are old enough 

 to change their color from white to brown or black ; after that it 

 is necessary to puncture the integuments. A combination of 

 anilin safranin and gentian violet gave the best results. 



MKGASPORES AND EMBRYO-SAC. 



The single archesporial cell is hypodermal in origin, and can be 

 easily recognized from the surrounding cells of the nucellus. 

 From this a single tapetal cell is formed, which may di\-ide again 

 either by anticlinal or periclinal walls ( F'igs. i, 2/'). In a very 

 few cases three tapetal cells were observed (Fig. 2d). Four 

 megaspores are formed in the usual manner (Figs. 2a, 2d). The 

 lower or functional megaspore enlarges at the expense of the three 

 potential megaspores and the tapetal cells (Fig. 3). The func- 

 ti<jnal megaspore now enlarges, giving rise to the two, four and 

 eight celled embryu-sac in the usual manner (Figs. 4, 5, 6, S). 

 In the four-celled stage the nuclei are approximately equal hi 

 size. In the eight-celled sta<4e the synergids are \ery large and 

 pear-shaped, and at least one persists until a very late stage in the 

 development of the embryo ( F'igs. 9, 10, 12, 13, 14, 16, 18). The 

 egg is slightly larger than the synergids and very similar in 

 appearance ; while the polar nuclei are comparatively large (F'igs. 

 6, 7). The antipodals are somewhat smaller and cut oft" from the 

 sac by delicate but definite walls (Fig. 6), and always occupy 

 about the .same relative position to each other. 



Contributions from the Botanical I.aboratory of Ohio State University. X. 



