ROOT 



that is, as acropetal branches of another root — they are 

 said to be adventitious. The difference between adventi- 

 tious and normal lateral roots is well illustrated by considering 

 the rOot-system of Dicotyledons and Monocotyledons. One of 

 the general characteristics of a Dicotyledon is that its embryo 

 in the seed has two cotyledons {e.g. Bean, Hazel, Oak). 

 Frequently the root-system of Dicotyledons is formed after 

 the manner described as occurring in the Bean, and well 

 illustrated by fig. 4. The embryo of a Monocotyledon, on 



Fig. 5. — Development of a typical Monocotyledon. 



the other hand, possesses only one cotyledon {e.g. Grasses, 

 Lilies). Nearly always the root-system of a Monocoty- 

 ledon develops in a manner entirely different from that 

 pursued by the Bean. The young primary root (r) of the 

 embryo grows for a short time only and produces at the 

 most few lateral roots, eventually shrivelling up ; but, sooner 

 or later, lateral roots arise successively higher up the stem, first 

 on the hypocotyl (a), then on the stem {a) — as is denoted 

 in fig. 5. Consequently, in full-grown Monocotyledons 

 practically the whole root-system is adventitious, and there 

 is no main-root with branches. [In fig. 5 the roots have 

 pulled the base of the shoot down into the soil.] 



