^38 



PRIMARF ARRANGEMENT OF TISSUES. 



711 



i 



JJ' 



Sometimes only one marginal bundle unites with the median, sometimes neither. 

 ,^ These 3, 4 or 5 bundles of a trace rarely run unaltered through 



the stem : the appearance of a trace is varied by occasional 

 splittings and reunions, so that it may retain 3-5 bundles (with 

 a width of ^th to ^th of the circumference of the stem), or be re- 

 duced to 2 or I bundle. The leaf-trace may be followed through 

 6-8 internodes, but further down it is impossible to recognise 

 with certainty how many bundles belong to each leaf. Within the 

 first 5 internodes no crossing or uniting with lower leaf-traces has 

 been observed. To this type belong Impatiens Bahamina and 

 Scopolina atropo'ides (Nageli). 



3. Leaves spirally arranged. Leaf-trace of five bundles, 

 pectinating with the third or fifth. Cocculus laiirtfolius (Nageli). 



4. Leaves spirally arranged. Leaf-trace of three bundles 

 which pectinate with the second and third. 



Lupinus Lehmann'i, Hort, and L. Inters, 'L. (Figs. 94, 95). 

 In the seedling a pair of opposite primordial leaves, or first 

 foliage leaves alternates with the two cotyledons. The second 

 pair of foliage leaves, of which one is inserted rather lower and 

 develops earlier than the other, alternate with the above, and 

 are thus opposite the cotyledons. The two leaves of the third 

 pair are not only at an unequal height, but also show a distinct 

 horizontal deviation from the opposite arrangement. The 

 fourth pair is intermediate between an opposite and spiral ar- 

 rangement ; all later leaves are arranged in a spiral. 



Each cotyledon has a leaf-trace of two bundles {a, h), which 

 become united into one in the lower portion of the hypocoty- 

 ledonary stem. Sometimes there is found a third weaker bundle 

 between the two bundles of one cotyledon. All later leaves have 

 three bundles. Those of the primordial leaves, which will be called 

 III and IV {c, d, e, f, g, h), are concomitant with the coty- 

 ledonary traces, so that a transverse section in the upper portion 

 of the hypocotyledonary part shows 10 bundles, two being op- 

 posite two, and three opposite three. The median bundles (/, m) 

 II of the second pair of leaves (leaves V, VI) pass downwards 



I through two internodes: on arriving at a median point above 



I H the trace of the cotyledons they curve, the one to the left the 



I I other to the right, and converging with the lateral bundles of 



■ H trace No. Ill, they immediately insert themselves upon them. 



Later a second rather weaker shank {v, x) is formed on each : 

 this curves, above the trace of the cotyledon, to the opposite 

 side, and is inserted on the opposite lateral bundle of leaf No. IV. 

 The lateral bundles of the pair of leaves V and VI {Ik, on) 

 descend through one internode, and cross the lateral bundles from 

 III and IV at the next node; in the following internode they lie 

 at the inner side of these, and are inserted upon them at the 

 cotyledonary node, or rather lower. 



The median bundles {p,q) of the third pair of leaves, VII 

 and VIII, pass through two internodes, and pectinate there with 

 the traces from III and W : p lies between the median and the 

 ascending, or anodic lateral bundle from IV, 9 between the median 

 and descending, or kathodic lateral bundle from III. They are 

 inserted on the above lateral bundles in the third internode. The 

 median bundle from leaf No. IX (r) applies itself to the ascending side of that of leaf 

 No. VI (w), that from leaf No. X (j) to the ascending side of that of leaf No. V (/). 



i-ig- 94- 



I-'g- 95- 



Figs. 94. 93. — I.upinus Leh- 

 manni, after Nageli. Fig. 94. 

 Scheme of the course of bundles 

 of a seedling, the cylindrical sur- 

 face being exposed in one plane ; 

 seen from within. — Fig. 95 (10). 

 Transverse section through the 

 stem above the cotyledons. The 

 letters the same in both figures. 



