FLOWERS OF I.UPA TIE.WS FULVA 169 



layers, at an early stage become elongated and tracheid-like (Fig. 17). 

 After fertilization the sac begins a rapid elongation, crushing the 

 tracheid-like cells below, and apparently absorbing their contents for its 

 growth. The elongation continues to the bottom of the ovule, then 

 turns and grows a short distance in to the funiculus. At its greatest 

 development, the embryo sac is thus a long narrow structure sharply 

 cur\'ed at its lower end (Fig. 36). 



The conditions in /. pallida seem to be in some points exactly the 

 same as in fulva. To judge from Miss Riatt's figures 1, J and K, and 

 2 L, the nucellus surrounding the embryo sac is one layer in thickness. 

 The cells below the sac are in three rows, which with the extension down- 

 ward of the lateral layers above make five rows. The cells show the 

 same elongated tracheidal form, and like fulva extend downward and 

 curve into the funiculus. The degeneration of the peripheral layer 

 begins apparently in the megaspore stage (Riatt, fig. 1 J). In the fer- 

 tilization stage the nucellus is apparently entirely gone at the sides and 

 micropylar end, and the embr\'o sac is against the jacket layer (Riatt 

 Figs. 2 and S). 



The cleistogamous pistil is similar in development and structure 

 except for a certain reduction. It arises in the same manner at first 

 as three papillae and later as a ring of tissue. The septa advance from 

 the side walls to meet the central placenta, dividing the ovary into five 

 chambers. In the pseudocleistogamous flowers the five little teeth 

 surmounting the very short style are much reduced or even absent, 

 and in the cleistogamous flowers they are generally absent entirely. 

 The stylar canals are present as in the chasmogamous flowers. In the 

 pseudocleistogamous flowers the full number of ovules may be present, 

 but in the cleistogamous flowers these are reduced to three, two or one. 

 The reduction of the number of seeds in the cleistogamous capsules is 

 not due to failure of fertilization or subsequent degeneration, but to a 

 reduction in the number of ovules which arise. The archespofial cell 

 divides to form four megaspores, and the chalazal spore persists. Some 

 sections show only three megaspores apparently, through failure of one 

 daughter cell to divide; often, however, the four megaspores appeared 

 in a linear series. The embryo sac forms eight nuclei, and the antipodals 

 and synergids are cut off as in the chasmogamous flowers. The mature 

 sac contains the egg and below it the two polar nuclei. The history 

 of the nucellus and integuments is the same as in the chasmogamous 

 ovule. 



As in other cleistogamous species, the pistil of the cleistogamous 

 flower differs from that of the chasmogamous chiefly by reduction^of 



