VEGETA TIVE^REPROD UCTION. 



20 1 



a spore. Because an embryo appears later inside this ap- 

 parent cavity, the megaspore of seed plants has long been 

 called the ^embryo-sac. 



The spore case is surrounded by one or two integuments. 

 These arise as outgrowths from the parts adjacent. If the 

 spore case is to have two coats, 

 the inner appears first as a low 

 ring around its base gradually 

 growing up around it; the outer 

 shortly appears in the same way 

 (fig. 159). These integuments, 

 as well as the spore case, often 

 grow unsymmetrically, so that at 

 the maturity of the megaspore the 

 ovule is often variously curved 

 (figs. 159, 160). The megaspore 

 itself may be distorted by this means so as to lose still more 

 its likeness to a spore. 



Ovules are borne either upon the axis itself or upon 



Fig, 



5g. — Two very young ovules 

 of the California poppy {Esck- 

 scholtzia\, seen from the outside. 

 fi, somewhat older than A . nc, 

 the rudiment of the spore case ; 

 j'c, rudiment of the inner integu- 

 ment ; pr, rudiment of the outer 

 integument ; fn, the stalk. Mag- 

 nihed 140 diam. — After Duchartre. 



Fig. i6g. —Diagrams of median longitudinal sections of three sorts of ovules to show 

 curvatures due to unsymmetric growth. A^ a straight, B, an inverted, C, a bent ovule. 

 In all : y^ the stalk ; A, the spore case; ii, the inner integument; ai, the outer in- 

 tegument ; OT, the micropyle ; c, the base of the spore case where the integuments 

 anse (called tlie chalaza) ; r, ihe ridge (rhaphe) formed by the union of stalk and outer 

 integument ; em, the megaspore. As C develops further em may become sharply 

 bent on itself.— After Prantl. 



the carpels. It is usual for the ovules to arise upon a car- 

 pel, either singly or in clusters, from a cushion or ridge, 



