118 MINUTE STRUCTURE OP THE STEM. 



Neither in Muscinese nor Thallophytes are flbro-vascular bun- 

 dles found, altliough in the former the arrangement of elongated 

 cells sometimes resembles that of the constituents of a simple 

 fascicle. The root-like bodies by which large sea-weeds cling 

 to their supports are hold-fasts, rather than true roots; the 

 whole surface of the plant being bathed in water, all parts can 

 probably absorb equally well. 



THE STEM. 



356. That part of the axis of the embryo which is below 

 the cotyledons is known as the radicle. It is more properly 

 termed caulicle (that is, stemlct), for its mode of growth is 

 not like that of the root, but like that of the stem above the 

 cotyledons. The name rndkie should be restricted to that 

 which is the beginning of the root, namely, the free end of the 

 caulicle. The caulicle is termed also the hypocotyledonary stem, 

 or hypocotyl ; while for the axis which is developed above the 

 cotyledons, that is, from the plumule, the name epicotyledonary 

 stem may be used. A large hypocotyl, wiiich has begun to 

 germinate, display's the structure of the stem to good advantage ; 

 but the initial cells and the nascent tissues of the stem must be 

 sought at an earlier stage, for instance, in the plumule of a well- 

 formed embrjo, as that of Phaseolus or Faba. A vertical section 

 through the plumule, made transparent b}- a clearing agent (see 

 24), shows that the cells have much the same arrangement as in 

 the root-tip, except that no protective cap is present. 



357. The outer layer has divisions onlj- at right angles to the 

 surface ; it is continuous with the epidermis further back, and 

 is easily recognizable as nascent epidermis (Dermatogen). En- 

 closed b}' this are layers which form an arch, the nascent cortex 

 (Periblem). This encloses a mass of tissue from which the fas- 

 cicular system is derived (Plerom). These tissues are essen- 

 tially the same in character and development as the corresponding 

 nascent tissues of the root. 



358. As the tissue elements develop from these nascent tis- 

 sues, the stem is produced ; its structure is, however, generally 

 complicated by the early foi-mation of lateral appendages, — leaves 

 in some of their modifications. Moreover, the tissues of the 

 stem are continuous with the tissues of the leaves, and it is there- 

 fore necessary to take into account the mutual relations of these 

 two organs. The problem becomes still further complicated, in 

 a large number of cases, liy the production of branches of some 



