THE MOLECULAR FORCES IN PLANTS. 



165 



but are distributed through the whole ground tissue. The cells 

 of this last are very large, and our attention is at once arrested 

 by the somewhat large intercellular spaces which appear as tri- 

 angular lacunce between the cells. Each of the collateral vascular 

 bundles is surrounded by a sheath of thick-walled sclerenchyma 



FIG. 56. Transverse section through a vascular bundle from the inner part of an inter- 

 node of the stem of Zea Mais, a segment of an annular vessel ; sp, spiral vessel ; m and 

 in', vessels with simple pits ; v, sieve tube ; s, companion cell ; cpv, crushed primary phloem ; 

 I, intercellular passage ; vg, sheath ; /, cell of the ground tissue. Magn. 180. (After Stras- 

 burger.) 



cells closely packed without intercellular spaces. In the phloem 

 of the vascular bundles the sieve tubes are visible ; w r hile in the 

 xylem several large vessels at once strike the eye. On the inner 

 side of the vascular bundle we observe a wide intercellular space. 

 'I'll is is of lysigenetic origin, while the intercellular spaces of the 

 ground tissue are developed schizogenetically. 



If transverse sections of the stem of Juncus glaucus are 



