446 UMBELLIFEILE 



contracts also and the cotyledons, which were originally some 

 distance above the soil, now lie close upon it. 



Soon thickening commences, both in the primary root and hypo- 

 cotyl, and as adventitious roots make their appearance from the 

 internal tissues of the latter, the distinction between the stem and 

 the true primary root becomes rapidly obliterated so far as external 

 appearances are concerned. In some field carrots a good deal of 

 the hypocotyl continues to grow above ground, thus resembling 

 mangels and turnips. 



On good soils the primary root extends to a considerable depth, 

 but only the upper portion of it becomes thickened ; the lower 

 part, which is left in the ground when the 'carrot' is pulled or 

 dug up, is long, thin, and cord-like, and bears many fine branch- 

 ing rootlets. 



As in the case of all fleshy farm ' roots,' except kohl-rabi, the 

 ' root ' of the carrot, for which the plant is cultivated, consists of 

 hypocotyl and root combined, the relative amount of each vary- 

 ing in different ' races ' or ' strains ' of the plant. 



On the outside of the 'carrot' are seen delicate secondary 

 roots which are arranged in four longitudinal rows ; but on account 

 of irregular growth the rows do not always remain straight. 



The thickened fleshy 'root' of the carrot, like that of the 

 turnip, presents the same general arrangement of tissues as is 

 met with in ordinary typical dicotyledonous roots and stems : 

 the differences consist in the abnormal development of the 

 elements composing its tissues. 



A transverse section of a carrot (2, Fig. 136) shows a layer 

 consisting of parenchymatous bast and secondary cortex (d), 

 which is wide in comparison with that of the turnip ' root,' and 

 of red or scarlet hue in red varieties. In the centre is the 

 ' core ' of wood (a), generally yellowish or dull white in colour. 



The relative proportion of wood to bast varies in different 

 ' races ' of carrots ; the endeavour of the plant breeder is to 

 obtain a relatively wide cylinder of bast {d) and a small core, 



