PHAXEROGAMIA. 



399 



the macrosporangiuin, where the coats and the tissue of the 

 sporangium proper become indistinguishable, is termed the 

 chalaza. The macrosporangium is not, as a ride, embedded in the 

 placental tissue, and is sometimes borne on a longer or shorter 

 stalk, the funicle. The point of attachment of the macro- 

 sporangium, whether it be sessile or stalked, to the placenta, is 

 termed the Jiilum. 



The form of the macrosporangium presents many varieties, of which 

 the following are the more common (Fig. 237). 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 anatropous ; when 



FIG. 237. Diagrams of the Ovule : A orthotropous (Polygonum) ; B anatropous (Lily) ; 

 C campylotropons (Bean): /funicle; of the outer integument; ti the inner integument; 

 m micropyle ; fc nucellus ; em embryo-sac : r the raphe ; c chalaza. 



the ovule itself is curved, so that the micropyle and the chalaza do 

 not lie in the same straight line, the ovule is campy lot ropous. 

 Various intermediate forms occur which may be easily imagined. 



The archesporium (see p. 53), which here, as elsewhere, is hypo- 

 dermal, consists generally of one cell. In some cases the arche- 

 sporial cell undergoes no division (e.g. Tulipa Gcsni-riana, Lilium 

 bulbiferurn) but directly developes into the mother-cell of a 

 macrospore ; but, as a rule, the archesporial cell (or cells) under- 

 goes 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) of the macrosporangium or sometimes two such 

 sterile cells which, with or without further division, represent a 

 tapetal layer. The large remaining cell now undergoes division 



