i.-jG 



THE STRUCTURE OF ECONOMIC PLANTS 



The companion cells are frequently divided transversely, espe- 

 cially in the secondary phloem, so that there may be two to a sieve 

 tube. Another variation occurs when the mother cell divides more 

 than once longitudinally, forming two companion cells and one 

 sieve tube. The former may divide transversely so that four com- 

 panion cells abut one sieve element. Chloroplasts occur in the 

 cytoplasm which is vacuolate. The phloem parenchyma is not 



specialized; and frequently exhibits 

 meristematic potentialities in general 

 cell division and in cambium forma- 

 tion, as it does in the root and stem. 

 Floral Development. — The gen- 

 eral habit of the floral axis and the 

 inflorescences has been described. 

 (Fig. ii8.) The sessile flowers which 

 occur either singly or more com- 

 monly in clusters of two or three 

 are small and greenish in color. 

 (Fig. 137, C) They are perfect and 

 have a five-parted calyx, five stamens, 

 and a pistil consisting of three car- 

 pels. The calyx is incurved, adherent 

 to the base of the ovary, and be- 



^, single^mature flower ^^^^^ j^^^j -^^ ^.J^^ £j.^ij. -pj^^ ^^^_ 



mens are inserted at the base of the 

 calyx lobes and opposite them. 

 They are introrse, bilocular, and 

 with young embryo; F, flower with dehisce by means of longitudinal 



mature embryo : g/.^^X glandular disc. ,■ Thp nkfil n<;nallv rnnsisrs nf 



(After Artschwager, >«r. ^gr. R^j.) ^^^^^- ^^^ V^^^^^ USUally COnslStS Ot 



three carpels, but occasionally there 

 may be two, four, or five. The half-inferior ovary is sunken in 

 a fleshy disk, and the very short style is terminated by two to 

 five awl-shaped stigmas. A single campylotropous ovule is at- 

 tached laterally to the ovary wall by a short funiculus. 



Payer (14) studied the floral development of Beta maritima and 

 the development in the sugar beet as reported by Artschwager (i) 

 agrees with it in all essential details. 



"The rudiments of the young flowers appear close behind the growing 

 points of branches of the inflorescence axis. Each rudiment is borne 

 in the axil of a large bract and is accompanied by two lateral bracts 



sligma 



Fig. 137 



viewed from above ; B, flower with 

 stamens already dropped ; C, cluster 

 of flowers attached to branch of in- 

 florescence axis and subtended by bract ; 

 D, flower after fertilization ; £, flower 



