98 MERISTEMATIC SYSTEM 



for special enquiry and one which in any case falls outside the scope 

 of the present discussion to what extent and for what length of 

 time an individual cell of the procambium retains the capacity for 

 giving rise, according to circumstances, to one or other of a whole 

 series of different permanent elements, such as stereides, segments 

 of wood -vessels or sieve-tubes, tracheides, phloem-parenchyma cells 

 and so forth. A similar uncertainty prevails with regard to this 

 point in the case of all meristematic tissues. 



3. Fundamental meristem or ground-meristem is the name given 

 to the whole of the primary meristematic tissue that remains un- 

 differentiated, after the protoderm and all the primary procambial 

 strands have been segregated (Fig. 22, m). In contrast to the pro- 

 cambium, the fundamental meristem is parenchymatous and relatively 

 large-celled ; it is, moreover, usually pervaded by conspicuous inter- 

 cellular air-spaces. The last-mentioned characteristic provides a 

 somewhat obvious point of distinction from the primordial meristem, 

 the cells of which are generally in uninterrupted contact with one 

 another at every point. As a rule, both the protoderm and the 

 procambium agree with the primordial meristem in being entirely 

 devoid of intercellular spaces. 



The fundamental meristem gives rise to the bulk of the paren- 

 chymatous permanent tissues such as the photosynthetic elements, 

 a part of the conducting parenchyma, the pith, etc. ; from the purely 

 anatomical point of view, these tissues may be collectively termed 

 the " fundamental parenchyma " or " parenchymatous ground-tissue " 

 in contradistinction to the " fascicular tissue " which comprises the 

 vascular and mechanical bundles or strands. But just as the pro- 

 cambium exceptionally produces parenchymatous elements, so the 

 fundamental meristem occasionally gives rise to fascicular tissue. An 

 interesting illustration is provided by the young scape of Allium, in 

 which, as the author has shown, the mechanical cylinder is derived 

 from the fundamental meristem, at any rate in the majority of species. 



IV. SECONDARY MEEISTEMS. 



Secondary meristems typically originate within living permanent 

 tissues which have previously been concerned for some time with a 

 specific vegetative function. The physiological properties of the new 

 permanent tissue or tissue-system produced by a secondary meristem 

 are, as a ride, quite different from those of the parent permanent 

 tissue. The activity of a secondary meristem thus frequently leads to 

 a far-reaching change of function. 



Among the various permanent tissues, it is the different kinds 



