!)0 



MERLSTEMATIC SYSTEM 



of view, however, the root-cap may, in a case of this kind, be regarded 

 as a mere proliferation of the protoderm ; this latter interpretation, 

 which was long ago adopted by Hanstein, is undoubtedly more in 

 accordance with the probable phylogenetic origin of the root-cap than 

 the conception of a primitive dermocalyptrogen. The second type of 

 structure is exemplified by the majority of Dicotyledonous roots ; the 

 following instances, among others, have been examined in detail: Heli- 



Fk; L9. 



Longitudinal section through the growing-point of the radicle of Hetianthus annuus. 

 Ii-h, root-cap : b-b, protoderm ; n-w, pericycle (pericambium) ; p-p, plerome. After 

 Keinke (from Sachs, Text-book). 



antlius annuus (Fig. 19), Fayopyrum, Brassica, Sinapis, Salix, Linum, 

 Cyclamen , Lysimachia. 



Type .">. In addition to the protoderm, the adjacent cortical layers 

 also take part in the production of the root- cap. Hence, on following- 

 up the protoderm towards the apex one does not, as in the preceding- 

 case, arrive at the inner limit of the root-cap, but, on the contrary, 

 penetrates more or less deeply into the substance of the cap. It must, 

 however, be noted that it is only the outer layers of the cortex or 

 periblem that contribute to the formation of the root-cap. According 

 to Flahault the roots of Cercis Siliquastrum, Gymnocladus canadensis, and 

 Juglans regia belong to this type. 



Type 4. The point of origin of the root-cap is more deeply seated 

 even than in the preceding type ; the entire cortical meristem, namely, 

 gives rise to the root-cap, while the protoderm remains undivided. 

 This type is illustrated by Acacia, Mimosa, Tamarindus, Gaesalpinia 

 and Lupinus, and by the Gymnosperms. 



Type 5. The primordial meristem of the root-cap is fused with that 



