52 



BOTANY OF THE LIVING PLANT 



fact that each of the largest strands on entering the stem from the 

 leaf slants sharply inwards, but short of the centre it curves again 

 outwards, and gradually approaches the periphery. There it fuses 

 with other strands. As the strand is thickest in the middle of this 

 course, the consequence is that the strands appear fewest and largest 

 at the centre, and smaller but more numerous near to the periphery 



Fig. 31. 



Transverse section of a vascular strand from the internode of Zea Mais, a = annular 

 tracheid. sp = spiral tracheid. m, m' = vessels with bordered pits. v= sieve-tubes. 

 s= companion cells. cpr= compressed first tissues of phloem. /= intercellular space. 

 vg = sclerotic sheath. /= conjunctive parenchyma. ( x 180.) (After Strasburger.) 



(Fig. 29). Thus the difference between the arrangement of the 

 strands in Dicotyledons and Monocotyledons is not fundamental. 

 As a matter of fact the one type graduates by intermediate steps into 

 the other. 



Similarly the structure of the strand itself is on the same plan in 

 both, the most conspicuous difference being the absence of cambium 

 in the Monocotyledons. One of the larger strands towards the centre 

 of the stem of Maize shows features usual in them (Fig. 31). It is 



