SYSTEMATIC BOTANY OF PEAS. AND THEIR ALLIES 



15 



and leaves are marked by a narrow blotch of red. The 

 red color sometimes extends to the back of the petioles, 

 the angles of the stem, and to the points of attachment 

 of the leaflets and their margins. This red blotch is 

 an excellent and constant character of arvense and 

 some of its allies. On dried specimens, however, it is 

 not always obvious. 



The flowers appear with rather great regularity 

 at the same internode in a given strain. In many 

 varieties the first flower arises from the sixth leaf, rarely 

 lower down, in others the first flower comes from a 

 higher leaf. Flowers are then produced from every 

 subsequent leaf-axil. 



The peduncles arise from the axil of the leaf between 

 the stem and petiole. They are terete, hollow, and 

 variable in length. At the time when the flowers open 

 they are often scarcely longer than the stipules, but 

 often continue to grow until they may greatly exceed the 

 stipules. But the length of the peduncle offers little as 

 a specific character, except in a few cases. 



There may be 13 flowers, or in the case of the 

 Scottish or tufted Pea (Pisum sativum arvense 

 umbellatum and Pisum sativum hortense coro- 

 natum) which merely represents fasciation of the stem, 

 as meny as 4- 5 flowers are produced on a single peduncle. 

 The number of flowers, however, is not always character- 

 istic, peduncles with 1 flower and others with 2 flowers 

 may be found on the same plant, or a second flower may 

 be found in a rudimentary state. Where one flower is 

 produced the peduncle is prolonged into a kind of beak, 

 often as long as the pedicel. This beak is the blind 

 end of the peduncle, not a bract. Bracts are usually 

 missing at the articulated base of the pedicel, though 

 very small or obscure ones may be observed. 



When two flowers are developed on a peduncle 

 there can be no beak at the lower flower, but the peduncle 

 is prolonged and ends with a second pedicel, at the base 

 of which a beak and, usually, bracts can be found. 

 These bracts vary greatly in shape and size. They 

 may be subulate or larger and somewhat foliaceous, 

 roundish or ovate, entire or toothed, and about up to 

 1 cm long, or they may be small and divided in various 

 ways in the manner of the first rudimentary leaves on 

 the germinating stem, or they may resemble two minute 

 stipules. 



The flowers of the peas have a peculiar shape, 

 familiar to everybody and characteristic of a large 

 number of plants, the family of the Papilionaceae or 

 Fabaceae, popularly known as the Pea Family. 



First of all the pea flowers are zygomorphic, i. e., 

 they can be divided by only one line into two corre- 

 sponding or symmetrical parts. The calyx is green, folia- 

 ceous with a short green tube, somewhat oblique at the 

 base, its 5 lobes, each with a deep green midrib, longer 

 than the tube, and bilabiate. The upper lip consists 

 of two larger, broader, and somewhat recurved lobes, 

 while the lower lip is formed by three narrower and more 

 acuminate lobes which point forward. The upper two 

 lobes back the upper larger petal, the vexillum or stand- 

 ard, while the three lower calyx lobes subtend the wing 



and keel petals. In bud the calyx lobes are arranged 

 so that the upper two touch each other with their inner 

 margins, while their outer or lower margins are covered 

 by the two lateral lobes which in turn are subtended on 

 their lower or inner margins by the lower and outermost 

 fifth lobe. 



There are 5 clawed petals placed alternate to the 

 calyx lobes. The uppermost, the " standard " or " vex- 

 illum," is the largest. It is usually semicircular in 

 outline, attached between the two upper calyx lobes. 

 It is notched at the top in the middle and plicate or 

 furrowed inside from the notch to the base and corre- 

 spondingly keeled at the back. It is usually variously 

 colored and finely veined, but in Pisum sativum hor- 

 tense. it is pure white with fine green veins, and greenish 

 towards the base. In bud the standard is folded and 

 covers all the other petals. The base of the standard 

 follows the direction of the calyx tube, but is then 

 strongly bent upward. At this point the standard is 

 thickened by two corresponding green callous crests 

 inside which help to stiffen the petal and form an entrance 

 to the honey chamber. These crests fit into depressions 

 on each of the next two petals. 



These next two petals are called the " wings." 

 Each has a narrow claw and is abruptly broadened above 

 it, and has there the depression into which the crest of 

 the standard fits, as was just mentioned. These depres- 

 sions, however, are only the back of prominent knobs 

 on the inner side, which in their turn are tightly fixed 

 in depressions of the following lower petals. The blade 

 of the wings is roundish and much smaller than the 

 standard. In color the wings are also often different 

 from the latter. The wing petals enclose the next 

 two. 



These two last and lowest petals, " the keel " of 

 the pea-flower, are grown together except at the base or 

 claw. They form a kind of a hood or little boat which 

 conceals the pistil with the style and the stamens. The 

 suture of the two petals is sharp and somewhat winged 

 like a keel. It is curved upward and ends in a rather 

 acute point. At their base above the claw there are 

 two deep holes into which the knobs of the wings tightly 

 fit. This rather complex structure is much the same in 

 most flowers of the Pea Family, and is correlated with 

 the manner of cross pollination, which is mostly effected 

 by bees and similar insects. 



Within the petals are the stamens and the pistil. 

 The lower part of the stamens is united into a kind of 

 tube around the pistil and almost as long as this. This 

 tube is split at the top lengthwise, as only 9 out of the 

 10 stamens are united, the upper (10th) being free down 

 to its base. The free ends of the filaments are bent 

 upward and densely packed together with the style in 

 the pointed top of the keel. 



The pistil rises from the middle of the bottom of the 

 calyx tube. At its base it is contracted into a stalk, 

 then it is laterally compressed, obliquely lanceolate, 

 the lower side usually straight, and the upper one more 

 curved. It is formed by one carpel, the margins of 

 which meet on the upper or inner side of the flower 



