STEMS OF MONOCOTYLEDONS. 13S 



382. Brannei'^ has shown that the bundles in Palms do not 

 end bhndlj at their lower extremities upon the surface of the 

 stem, but that they are connected in sections or divisions from 

 base to summit one with another, and one on top of another. 

 He has further shown that each bundle Ues in a spiral curve 

 within which it grows ; and whether it returns to the surface 

 upon the side in which it originated or upon the opposite side, it 

 is always in this curve. 



383. The structure and development of monocot^^ledons have 

 received much attention during the last few years, and the 

 results obtained have caused some modification of previousl}' 

 existing classifications. Two of the proposed methods of re- 

 arrangement are herewith given : — 



384. Falkenberg recognizes the three following types of stems 

 of monocotyledons. 



I. The tissue of the central cylinder is not plainly separable 

 even in its mature state into conjunctive parenchyma and fi.bro- 

 vascular bundles. (To this type belong the water-plants, 

 Zostera, Potamogeton, and probably all submerged monocoty- 

 ledons.) 



II. The bundles and the fundamental tissue are plainly differ- 

 entiated ; the former extending almost horizontally from the 

 lea^'es to the middle of the cylinder, then curving downwards, 

 running outwards, and finally terminating in the superficial 



is assumed that tlie leaves alternate with precisely one half divergence, and in- 

 clude the stem, and that the threads stand tangentially perpendicular, then the 

 actual course in the stem will be shown in the plan of a radial section through 

 the median thread of a leaf given in Fig. 109. But the assumption of a radi- 

 ally perpendicular course is valid only for those bundles wliich are also tangen- 

 tially perpendicular. As was iirst observed by Meneghini, admitted afterwards 

 Ijy Mohl (Verm. Schrifteu, p. 160), and more minutely shown by Nageli, each 

 radially curving thread runs also in a tangentially obli(|ue direction, and 

 in spiral curves which are proportionate to the radial curving. Nageli found 

 the median thread of a leaf of Chaniiedorea elatior, Mart., for example, making 

 IJ revolutions in six internodes ; in the sixth, it liad not, in its outward course, 

 quite reached the middle point between the centre of the stem and the inner 

 surface of the bark. In stems with very short internodes and closely crowded 

 bundles the spiral curves are at once perceptible in the cross-section, being 

 plainest in the bundles of the stem of Xanthorrboea, which press almost hori- 

 zontally towards the centre of the stem, tliis peculiarity giving to its cross- 

 section the strange appearance which has been frequently mentioned. 



" Finally, raanj' variations from that course of a thread which has here been 

 described as typical may occur ; there may be curvings alternately toward 

 the outside and the inside, etc., which are not constant." 



' Proceedings of American Philosophical Society, 1884, p. 459. 



