Apical organization of the roots of dicotyledons

Summary and Conclusions

The root apical organisation of nine species of dicotyledons belonging to some primitive and some advanced families has been investigated.

The structural configurations of these species fall under three types: (i) with four superimposed tiers, a common tier for the dermatogen and the peripheral region of the root-cap—the dermocalyptrogen—hypodermis, periblem and plerome, (ii) with three tiers of initials, the dermocalyptrogen, periblem and plerome, and (iii) with a common group of initials for all.

InGrevillea roots, as they grow older, the cortical initials are found to divide obliquely and transversely towards the distal end at their junction with the columella, form secondary columella files which exhibit knees and thus contribute to the cap region. This shows that ontogenetic studies are required to understand fully the apical organization.

The presence of a common group of initials in the third type and its positionvis-a-vis the central cell and initial group concepts has been discussed.

The presence of two distinct sets of initials in the cap, one for the formation of the peripheral portion and the other for the columella, is discussed in relation to literature.

The formation of parabolas at the root apices leading to a distinct pattern formation is exhibited particularly by aquatic plants and the probable relation of the habitat to such is pointed out.

The different modes of origin of the epidermis and the origin of the endodermis are brought out.