94 MERISTEMATIC SYSTEM 



While the root-cap in the first instance serves to protect the 

 delicate primordial meristem of the root, it also acts as a boring-point 

 which helps the root to force its way through the soil. The root-cap 

 is able to perform this active function partly by virtue of its conical 

 shape, but even more on account of the fact that its cell-membranes 

 or at any rate the middle lamellae of the old superficial cells readily 

 become gelatinous ; the slimy surface which the root-cap consequently 

 acquires materially assists the root in overcoming the frictional 

 resistance of the soil-particles.' 3 In addition, the axile region or 

 " columella " of the root-cap harbours the statocysts or cells furnished 

 with movable starch grains, which serve for the perception of 

 gravitational stimuli. 



77/. THE PRIMARY MERISTEMS. 



In all the Higher Plants, the homogeneous primordial meristem 

 becomes differentiated, at a varying distance from the growing-point, 

 into several distinct meristematic layers, or primary meristems. To 

 begin with, this differentiation amounts to little more than a topo- 

 graphical separation of a dermal layer from the more central tissues, 

 accompanied by a segregation of " strands " or " bundles " from 

 parenchymatous ground-tissue : it affords little or no indication of the 

 nature of the functions that will be performed by the corresponding 

 permanent tissues. 



Such a differentiation of the primordial meristem into primary 

 meristems is not a peculiar condition associated with any one mode 

 of apical growth or dependent upon the presence of more than one 

 initial, but takes place in every organ that attains to a certain degree 

 of anatomical complexity in its adult condition. The following 

 classification of primary meristems devised by the author is therefore 

 equally applicable to the shoot of a Moss and to the stem, leaf, or 

 root of a Dicotyledon. 



In almost every case, three distinct primary meristems are present 

 [namely, protoderm, procambium and fundamental meristem]. 44 The pro- 

 toderm is the outermost meristematic layer (Fig. 22, p), and represents 

 the primitive dermal tissue of the young organ, though only in a, 

 topographical sense ; it exhibits none of the anatomico-physiological 

 characters of typical dermal tissues, and may not even necessarily 

 acquire these features when it becomes converted into permanent 

 tissue, since it not only gives rise to the epidermis but also regularly 

 produces the principal absorbing organs, and in certain cases also takes 

 part in the formation of mechanical or photosynthetic tissues. 



The precise genetic relation of the protoderm to the primordial 



