GROUP IV. — PHANEROOAMIA. 



437 



The macrosporangium is not, as a rule, embedded in the placental 

 tissue, and is sometimes borne on a longer or shorter stalk, the 

 funicle. The point of attachment of the macrosporangium, whether 

 it be sessile or stalked, to the placenta, is termed the hilum. 



The form of the macrosporangium presents many varieties, 

 of which the following are the more common. When the micro- 

 pyle, the chalaza, and the funicle (or the hilum) all lie in one 

 and the same straight line, the ovule is said to be orthotropous : 

 when the micropyle and the chalaza lie in the same straight line, 

 but not the funicle, the ovule being bent back against the funicle 

 (termed the raphe along the line of contact), the ovule is ana- 



Fi». 284.— Diagrams of the Ovulev J^ OrthotropouSv P Anatropous. C Campylotropous. 

 / Funicle; ai the outer integument; ii the inner integument ; m micropyle; fcnucellus; 

 em embryo-sac ; r the raphe ; e chalaza. 



tropous; when the ovule itself is curved, so that the micropyle 

 and the chalaza do not lie in the same straight line, the ovule is 

 campylotropous. Various intermediate forms occur which may be 

 easily imagined. 



The archesporium (see p. 73), which here, as elsewhere, is 

 hypodermal, consists generally of one cell, though sometimes 

 apparently of several lying side by side {e.g. Casuarina; some 

 Rosaceae, such as Rosa livida, Fragaria vesca, Cydonia japonica^ 

 Sanguisorba pratensis ; possibly also some Gyranosperms, Gnetura, 

 Taxus, Ginkgo, Thuja). In some cases the archesporial cell 

 undergoes no division (e.g. Tulipa Qesneriana^ lAlium hulhiferum) 

 but directly developes into the mother-cell of a macrospore ; but, 

 as a rule, the archesporial cell (or cells) undergoes more or less 

 frequent division. Thus, in most Phanerogams, the division of 

 the archesporial cell begins with the cutting off, by a periclinal 

 wall, of a sterile cell towards the organic apex (micropylar end) 



