146 



Elementary Biology. 



FIG. 64. Attiiim cepa. BULB. 

 (Edmonds.) 



shoot, which is elongated into a long axis on which the 

 flower is borne. Between the bases of the leaves we may 

 find buds or branch shoots about to give forth another floral 

 axis in the next season. The likeness to the underground 

 rhizome of the fern is thus again brought up. 



The floral axis presents a 

 more suitable subject for ex- 

 amining the structure of the 

 monocotyledonous stem than 

 the modified underground bulb. 

 If a section be made across it 

 it will show externally a colour- 

 less epidermis, enclosing a large 

 soft fundamental parenchyma 

 in which run the fibro- vascular 

 strands (fig. 65). The mode of 

 origin of these we shall notice 

 later on ; meantime it will be 

 sufficient to draw attention to 

 the fact that the smallest strands 

 are placed close to the epider- 

 mis, while they increase regu- 

 larly in size as the centre is 

 approached. There cannot be 

 said to be any distinct pith, that is, fundamental tissue left 

 unmodified in the centre of the stem, for there is no clear 

 line of demarcation between the fundamental tissue of the 

 centre and that between the several strands. The course of 

 the fibre-vascular strands in the stem may be best studied in 

 a longitudinal section, such as that represented at fig. 65 B. 

 There it will be seen (in an allied type) that the strands 

 pursue a wavy course, arising close to the outside of the 

 stem, curving inwards, and, after recurving outwards again 

 and crossing the strands higher up, pass out entirely into 

 the base of a leaf. These fibro- vascular strands when fur- 

 ther examined are found to contain elements similar in 

 general structure to those described in the stem of the fern, 



a, a, bu ds ; b, stem proper 

 which roots originate. 



from 



