SPERMATOPHYTES 
261 
the ovules may be foliar or cauline. In the different groups of angio- 
sperms, however, the ovules are borne in very definite ways. 
General structure. In the development of the ovule, the nucellus 
first appears as a protrusion from the surface which bears it; later a ring 
arises around its base, which develops into an integument; and still 
FIG. 581. Development of an anatropous ovule, the series beginning at the left; the 
two integuments appear successively and gradually overtop the nucellus as the ovule 
becomes curved; last figure a section showing relation of the two integuments and the 
nucellus at maturity of ovule. After GRAY. 
later a second ring may arise outside of the first, which develops into a 
second integument (fig. 581). Soon the integument (or integuments) 
overtops the nucellus, and where it closes in over the nucellus there is 
left a narrow, more or less elongated passageway, the micropyle (fig. 
582). Among the Archichlamydeae and monocotyledons there are 
582 
583 
I I 
FlGS. 582-584. Directions of ovules; 582, orthotropous; 583, campy lotropous; 
34, anatropous; also showing outer (of) and inner (it) integuments, micropyle (m), 
.irelltis (n) t and embryo sac (em). After COULTER. 
usually two integuments; while among the Sympetalae there is almost 
invariably a single massive integument. 
Direction. Important differences are shown in the directions as- 
sumed by mature ovules. Some grow straight outward from their place 
of origin, the axis being straight and the micropyle directed away from 
the point of origin; such ovules are called orthotropous (fig. 582), and this 
condition is regarded as the most primitive. In other ovules the axis 
