Vlll 



MARATTIALES 



283 



At first the growth is nearly vertical, but it soon becomes 

 stronger upon the outer side, and the leaf rufliment bends 

 inwards. At this stage the dififerent tissues begin to l>e dis- 

 tinguishable. Somewhat later the tip of the cotyledon becomes 

 flattened, and still later there is a dichotomy of this flattened 

 part which thus forms a fan-shaped lamina (Fig. 157). The 



Fig. 156. — Marattia Douglasii. A, B, C, Three transverse sections of a root from the 

 young sporophyte; A shows the apical cell (x), X215; D, longitudinal section of a 

 similar root, X260; E, vascular bundle of the root, X260. 



first tissue to be recognised is the vascular bundle w^hich 

 traverses the centre of the petiole and at first consists of uni- 

 form thin-walled elongated cells (procambium). This forma- 

 tion of procambium begins in the centre of the embryo and 

 proceeds in three directions, one of the strands going into the 



