24° 



PRIMARY ARRANGEMENT OF TISSUES. 



lower node, they traverse the next internode in conjunction with the median bundle of 

 the next upper leaf, and each inserts itself in the second node on an axillary bundle of 



. the next lower trace. The two axillary 

 bundles, dc, ik, op, tu, take an inde- 

 pendent course in their own internode, 

 in the next they combine with the 

 lateral leaf-bundles of the next higher 

 trace, and insert themselves in the se- 

 cond node on the lateral leaf-bundles 

 of the next lower trace. These con- 

 ditions are very regular : the transverse 

 section through an internode therefore 

 shows regularly 1 1 bundles ; Fig. 97 shows 

 the arrangement of these, and explains 

 them by means of the same lettering as 

 at the lower end of Fig. ^6. 



10. Leaves alternating in two rows. 

 The rows are nearer one side in the 

 terminal bud. Leaf-trace of 3 bundles, 

 which pectinate with the traces of both 

 rows. 



Medicago sativa, Lathyrus Nisiolia, 

 L. Aphaca and Pseudaphaca, L. Odoratus, 

 L, purpureus. 



L. Aphaca and Pseudaphaca (Figs. 

 98, 99). The leafy stems are four-cor- 

 nered, the corners are sometimes slightly 

 extended as wings. The transverse sec- 

 tion (Fig. 99) shows in each of the two 

 opposite lateral edges a bundle (h, g) and 

 internally a circle of 8 and more bun- 

 dles, which later decrease in number by 

 coalescence. The median bundle of the 

 leaf-trace divides as it emerges into the 

 leaf into 3 branches, of which the central 

 weaker branch enters the petiole, while 

 the lateral ones form bow-like anasto- 

 moses with the two lateral bundles : from 

 these arise the bundles for the stipules. 



The median bundle («,/, /, 0, r, u) 



runs separately down through two in- 



temodes, then curves to one side («), 



and later it forks into two shanks. These 



insert themselves on the lateral bundles 



of the next lower leaf-trace. The two 



lateral bundles (be, gh, mn, pq, it) run 



first in the comers through their own 



internode : at the next node they enter 



the circle of .bundles of the trace, where 



they pectinate with the lateral bundle of 



the next lower trace : each then unites 



with one shank of the median bundle of the next higher trace, and running together 



with It through two internodes, inserts itself finally in the third internode below on the 



lateral bundle of the second lower trace. 



i-ig. 98. 



Fig- 99- 



Figs. 98, 99.— Lalhyrus Pseudaphaca, after Nageli. Fig. 98. Scheme 

 of the course of the l)uiitHes in the apex of the stem supposed to be 

 transparent ; the bundles on the side further from the observer are 

 paler, those on the near side are black.— Fig. 99 (25), Transverse sec- 

 tion through an internode such as the lowest but one of Fig. 98 ; with 

 the same lettering as the latter. 



