THE MEGASPORANGIUM 63 



reduction in their number, although this is accompanied by a pro- 

 nounced radial elongation of the walls (Fig. 44Z)). In Oldenlandia 

 the micella r epidermis is represented by one or two cells only (Fig. 

 4AE), and in Houstonia, which is the last member of the series, there 

 is no distinguishable epidermis and the ovule consists of only the 

 sporogenous cells and the integument (Fig. 44i^). 



Fagerlind's series is so clear and convincing that there is no longer 

 any doubt about the true relationships of the nucellus and integu- 

 ment in the Kubiaceae. Houk's (1938) statement that in Coffea 

 there is no distinction between the tissues of the integument and 

 nucellus is therefore incorrect (see also Mendes, 1941). 



Woodcock's (1943) report that in Ipotnoea the ovule has no dis- 

 tinct integument and the micropyle is formed by an "invagination" 

 is also due to a misinterpretation. As in other members of the 

 Convolvulaceae (see Maheshwari, 1944), an integument is present 

 and it is the nucellus which soon disappears. The micropyle is 

 not an invagination but a continuous passage, which begins to be 

 more or less occluded in postfertilization stages and is therefore 

 difficult to demonstrate in nonmedian sections. 



Formerly the Olacaceae were also believed to have naked ovules. 

 A recent study by Fagerlind (1947) has shown that an integument 

 is present as usual but the nucellus is extremely reduced and ephem- 

 eral and is represented by only a few epidermal cells lying just 

 above the megaspore mother cell. 



A complete absence of the integuments is known only in some 

 members of the Loranthaceae and Balanophoraceae, but it seems 

 probable that this is a derived condition. Fagerlind (1945c?) has 

 given a series of illustrations showing the stages by which this may 

 have been brought about (Fig. 45). The case of Crinum (Amarylli- 

 daceae), in which the nucellus is ephemeral and the integuments are 

 said to be absent (Tomita, 1931), deserves further study. 



Integumentary Tapetum. In those plants in which the nucellus 

 is soon disorganized, the embryo sac comes in direct contact with 

 the inner layer of the seed coat. The cells of this layer frequently 

 become specially differentiated from the rest by their form and con- 

 tents (Fig. 46). They show a pronounced radial elongation and 

 sometimes become binucleate. Owing to these similarities with the 

 cells of the anther tapetum, this layer of cells is known as the integu- 

 mentary tapetum or endothelium. 



