Feb., 1908.] Embryology of Oxalis cornieulata. 261 



THE EMBRYOLOGY OF OXALIS CORNICULATA.* 



Howard S. Hammond. 



Oxalis cornieulata might be called a sub-tropical plant 

 although it is frequently found growing in ballast about the 

 Eastern seaport towns of the United States and becomes quite 

 abundant in Texas. In tropical America it is quite common and 

 is also reported as occurring in the tropical regions of the Old 

 World. It has been reported as far north as Ontario. Fre- 

 quently it is found growing on the ground in greenhouses where 

 it blooms profusely throughout the year. It was under these 

 last named conditions that the writer secured the material with 

 which he worked. The material was collected throughout the 

 Spring of 1906 and the Fall and Winter of 1906-1907. The 

 usual methods of killing and imbedding were used. The sections 

 were cut 8 mic. thick and stained on the slide. Delafield's 

 Haemotoxylin proved the most satisfactory stain. To Prof. 

 John H. Schaffner under whose direction this study was begun 

 and to Prof. Robert F. Griggs under whom the study was com- 

 pleted I desire to express my sincere thanks for their kind 

 assistance and suggestions. 



MEGASPORES AND EMBRYO SAC. 



The nucellus consists of a single axial row of cells invested by 

 the epidermis (Fig. 1). The uppermost cell of the axial row is 

 the archesporium which, thus appearing very early, increases to 

 two or three times its original size. It does not give rise to 

 parietal tissue but undergoes directly the Reduction Division 

 which was not observed (Fig. 2). The lowest of the three or 

 four megaspores thus formed becomes the functional one, and 

 rapidly enlarges at the expense of the potential ones above, giv- 

 ing rise to the two (Fig. 3), four (Fig. 4), and eight (Fig. 6), 

 celled embryo sacs in the usual manner. Before the two celled 

 embryo sac is formed the surrounding epidermis which functions 

 as tapetum, has begun to disintegrate and the sac is subsequently 

 enclosed simply by the integuments. The embryo sac develops 

 very rapidly and is nearly straight although the ovule is anatro- 

 pous. The antipodals are small, stain darker than the polar 

 nuclei or the unfertilized egg, and begin to disintegrate at the 

 time of the conjugation of the polar nuclei (Fig. 6), sometimes 

 disappearing before fertilization in case that is delayed till after 

 the polar nuclei have fused (Fig. 5). The synergids stain dark, 

 are rather large, and also disintegrate early, one of them being 

 destroyed by the entrance of the pollen tube (Fig. 6). 



ENDOSPERM AND EMBRYO. 



Connecting the endosperm cells are radiations, as has been 

 frequently observed in many plants, but these are not kino- 



* Contributions from the Botanical Laboratory of the Ohio State University, XXXIII. 



