RAPHANUS SATIVUS z8^ 



soil produces large laterals. These may extend horizontally to 

 distances of 3 feet or more on all sides of the plant, branching pro- 

 fusely and forming a network of rootlets. In the Long Scarlet 

 type, by the time the upper portion of the root has reached market- 

 able size, it may have penetrated to depths of 3 feet with much- 

 branched laterals which spread radially to distances of 2. feet. The 

 mature plants are characterized by tap roots 43^2 to 5 feet long with 

 many major laterals in the surface foot of soil which frequently 

 extend outward to a maximum of 40 inches. They in turn may 

 give rise to branches which penetrate the soil deeply; and, as a 

 result, the surface soil is well filled with roots while the subsoil 

 also contains numerous branched laterals. 



The Hypocotyl. — The upper portion of the fleshy primary axis 

 is practically devoid of lateral roots, consisting of a thickened 

 hypocotyl which is transitional in its vascular organization. The 

 relative proportion of the lower part of the axis which can be re- 

 garded as the root is greater in the case of the half-long or long 

 icicle varieties than in the globe types. Golinska (6) interprets 

 the fleshy portion as a transition region and regards it as being 

 more root-like than stem-like. (Fig. 141.) There is a reorienta- 

 tion of the vascular elements in the upper limits of the hypocotyl, 

 but the endarch relationship is not attained at the cotyledonary 

 node, and exarch strands extend into the cotyledons as in the 

 potato. 



Although it has been demonstrated genetically by Malinowski 

 (10), Moldenhawer (li), and Sutton (19) that the development 

 of the fleshy axis is a hereditary characteristic, external factors, 

 especially length of day, have a marked influence upon the degree 

 of its development. Sinskaja (17) found that varieties brought 

 from China, Mongolia, Japan, and India produced no thickenings 

 and bloomed the first year when grown in greenhouses in Lenin- 

 grad; but when the photoperiod was reduced to an interval of 7 

 to li hours, they became fleshy and bloomed much later or not at 

 all. Garner and Allard (5) obtained fleshy root-hypocotyl axes 

 with a 7-hour day, and with a ii-hour day were able to produce 

 seeds in the winter months. 



The Stem. — There are two phases in the development of the 

 stem. The first occupies the initial 4 to 6 weeks after germination 

 when a rosette of leaves develops from a short crown stem. The 

 second period is that during which the flower stalk is formed fol- 



