1902] ROOT-HAIRS, CAP, AND SHEATH OF AZOLLA 4^9 



EXPLANATION OF PLATE XVL 



All figures except figs, /, 2, 12, were drawn with the aid of the camera 

 lucida. 



Fig. I. Longisection of the growing apex of the stem in Azolla filicidoides 



(after Strasburger) : Ri, root initial ; si, sheath initial ; s, S', segments 



of sheath initials ; X 260. 

 Fig. 2. Fundament of the root in the same species (after Strasburger): AC, 



apical cell ; Ci, cap initial ; s, s^ outer and inner sheaths ; X 260. 

 Fig. 3. Longisection of a young root of A.filiculoides\ s, sheath ; cS c^ outer 



and inner caps; X 4So. 



Fig. 4. Longisection of the growing tip of a root of A. fi/tc?i/ozdes (microtome 



section from material embedded in paraffin) ; D, periclinal division at 

 apex of inner cap ; c^ C, outer and inner caps ; Ti, hair initial ; X 450. 



Fig. 5, Hair initials and intervening cells at the beginning of the growth of 



the hairs, about ten cell pairs removed from the oldest shown in 



7?^. ^ ; X 450- 



Fig. 6. First transverse division of intervening cell; X 45o. 



Fig. 7. Young root hairs seen in tangential section of the root, showing 



zonal arrangement ; X 450. 

 Fig. 8. Origin of the hair initials; close of mitosis and forming cell-plate are 



seen at d; X 750. 

 Fig. 9. Young hairs in radial longisection, separated in the row by four 



intervening cells ; X 300. 



Fig. 10. Base of mature hair, between elongated epiblema cells; X 450- 



Fig. I i. ^, initials at the edge of the root-cap, and B, relatively young hairs 



near the tip of the growing root of Lycopodium luciduliifft ; the arrow 

 shows the direction of the root apex ; X 4 50. A peculiarity of Lyco- 

 podium is that in most species the hair initials usually divide longi- 

 tudinally, so that the hairs stand in groups of from two to four. 



Fig. 12. Habit oi Azolla filicidoides ; X 5- 



Fig. 13. Terminal portion of root, showing cap and root-hairs; X 24. 



