58 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



completely absorbed and do not take any part in the formation of 

 the seed coat. In the Umbelliferae only two or three of the outer 

 layers persist at maturity; in the Compositae most of the cells dis- 

 appear, leaving only a thin layer of crushed and disorganized tissue ; 

 and in Circaeaster (Junell, 1931), Thesium (Rutishauser, 1937), and 

 Zea (Randolph, 1936) practically nothing remains of the seed coat. 

 In Symplocarpus (Rosendahl, 1909) both integuments and endo- 

 sperm are consumed so that the embryo lies naked inside the ovary 

 wall. So variable is the nature of the cell layers surrounding the 

 embryo that only a thorough study of the developmental stages can 

 reveal their true nature. 



Mention must be made of a few records of the occurrence of 

 chlorophyll in the integuments. Hofmeister (1861) observed this 

 in Brunsvigia minor and Amaryllis belladonna, and Treub (1879) 

 in Sobralia micrantha. Later, Berg (1898) and Puri (1941) reported 

 the presence of chlorophyll in the outer integument and a portion 

 of the chalaza in Gladiolus communis, Lilium martagon, and Mor- 

 inga oleifera. Schlimbach (1924) observed the presence of stomata 

 on the outer integument of Nerine curvifolia, and Flint and More- 

 land (1943) have described the occurrence of an elaborate chloro- 

 phyllous tissue with stomata in Hymenocallis occidentalis. Stomata 

 have also been found on the outer integument of Gossypium, but 

 they are believed to be concerned with respiration rather than 

 transpiration or photosynthesis (Seshadri Ayyangar, 1948). u 



Micropyle. When two integuments are present, the micropyle 

 may be formed either by the inner integument as in the Centro- 

 spermales and Plumbaginales (Fig. 38) or by both inner and outer 

 integuments as in the Pontederiaceae (Fig. 142). Less frequently, 

 as in the Podostemonaceae, Rhamnaceae, and Euphorbiaceae, it 

 may be formed by the outer integument alone (Fig. 67 A). When 

 both the integuments take part in the formation of the micropyle, 

 the passage formed by the outer integument (exostome) may not 

 be in line with that formed by the inner integument (endostome) 

 so that the micropylar canal has a somewhat zigzag outline. Good 

 examples of this kind are seen in the Resedaceae (Oksijuk, 1937) 

 and in some members of the Melastomaceae (Subramanyam, 1948). 

 In Leitneria (Pfeiffer, 1912) and Malpighia (Subba Rao, 1941) there 



la See Boursnell (1950) on the occurrence of a fungus in the funiculus and outer 

 integument of Helianthemum chamaecistus. 



