14 



THE VEGETABLES OF NEW YORK 



crosses between such races occurred spontaneously 

 through the agency of insects. The individual races are 

 separated by slight and often variable characters. The 

 species, subspecies, or varieties which we more or less 

 arbitrarily adopt for our convenience are composed of 

 many such races. If extreme forms are singled out, it 

 seems as if they could be considered as sufficiently 

 distinct " species " but as soon as large numbers of 

 specimens are taken into consideration no single char- 

 acter proves constant and the supposed " species " 

 may be segregated into an almost endless number of 

 smaller races or strains. S. T. Wellensick ' admits 

 concerning I'. sativum bortense, 1'. sativum arvense, 

 I'. sativum elatius, and 1*. sativum Jomardii that 

 there " are at least 500 constant strains, which after 

 crossing iso far as they have been studied) produce 

 invariably fertile hybrids. As recombinations are con- 

 tinually being produced by crossing, it is evident that a 

 division of the genus Pisum into a small number of 

 species cannot stand the test of time. Therefore it 

 would seem a rational proceedure to combine into one 

 species all the cultivated forms of Pisum that are mutu- 

 ally crossable." 



This was first done by Alefeld (Landwirtsch. 

 Flora 1866>, who. however, gave Latin varietal names 

 to all the 102 wild and cultivated varieties or races known 

 to him. Ascherson & Graebener admit as subspecies 

 V. sativum elatius, I'. sativum arvense, and I*. 

 sativum hortense. There are, however, as is evident 

 from what was said above, no clear differences between 

 subspecies and it is not always easy to say with which 

 subspecies a given individual plant should be classified. 

 P. sativum elatius sometimes closely resembles P. 

 sativum arvense; I*. sativum Jomardii seems to 

 come very near to I'. sativum abyssinicum; and P. 

 sativum syriacum approaches P. sativum elatius. 



Pisum fulvum is the only one of all the annual 

 peas, so far known, that has sufficiently distinct char- 

 acters to admit it to the rank of a species. 



Western Asia, from Syria and Asia Minor to the 

 east, is the region where most of the forms of Pisum are 

 to be found in a spontaneous, subspontaneous or culti- 

 vated state. I'. sativum elatius has extended west- 

 ward spontaneously into the Mediterranean region and 

 southern Europe, and P. sativum ar\«-use exists in 

 Italy as a wild, not as an escaped plant. 



The germination of the pea is subterraneous, the 

 cotyledons remain included in the seed coat, which 

 opens only enough to allow the young root and stem to 

 grow. The root immediately sends out numerous 

 smaller lateral rootlets. The stem is almost terete at 

 first and bears two rudimentary or primary leaves, of 

 w-hich the first one is subterraneous. The second leaf 

 covers and protects the stem at the curved point with 

 which the plantlet penetrates the soil. These first 

 rudimentary leaves show clearly two lateral ovoid 

 blades, corresponding to the stipules, and a narrower 

 middle part, sometimes with a very small hooked point, 



evidently representing the petiole, rhachis, and tendril 

 of the later perfect leaves. In many cases, later on, a 

 lateral stem is produced from the axil of the upper 

 rudimentary leaf. 



With the appearance of the leaves the stems become 

 4-angled. Two of the angles run down from the 

 midribs of the two stipules and one from the petiole. 

 The angle of the latter covers two internodes. The 

 stems are weak, soft, and hollow inside, and the inter- 

 nodes are more or less flexuous. 



The leaves are distichous and alternate, i. e., they 

 stand in two opposite rows, one above the other. Stip- 

 ules are always present. In Pisum formosum, the 

 only perennial pea extant, so far as we know, they are 

 small. In the annual peas, subgenus Lophotropis, 

 however, the stipules are much larger from the begin- 

 ning; and though comparatively smaller on the lower 

 leaves they reach a considerable size on the upper part 

 of the stem and exceed the leaflets. The stipules are 

 clasping, obliquely attached, the lower part often 

 overlapping, and the outer margin dentate, at least 

 near the base. The stipules form an excellent protection 

 for the tender growing points of the plant and the young 

 flower buds. In Pisum sativum hortense they are 

 usually rounded at the top with a small cusp, while in 

 P. sativum arvense they are usually more pointed. 



In Pi.su in formosum, the petioles are channeled 

 on the upper side, have one pair of leaflets and terminate 

 in a small cusp representing a primitive tendril. The 

 channeled petioles and the small stipules seem to be 

 very old characters, which in P. formosum remain 

 constant while in the annual peas, these characters are 

 observed only in juvenile plants and in the lower leaves 

 which have a distinctly channeled petiole, a little 

 longer than the small stipules and one pair of opposite, 

 entire, or indistinctly toothed leaflets, usually notched 

 and with the midrib mostly protruding into a small 

 cusp. The petiole ends in a short primitive tendril, a 

 few millimeters long, much resembling that of P. 

 formosum. At about the 3rd or 4th leaf the tendril 

 begins to lengthen and branch into 1-3 pairs of lateral 

 branchlets; and, at the same time, the petioles become 

 terete or almost so. Very rarely the tendril is not 

 developed at all, as in the case of the remarkable variety 

 " Acacia." This has four pairs of leaflets and a terminal 

 odd leaflet, but no trace of a tendril. Rudimentary 

 tendrils and channeled petioles, however, are found on 

 the lowest two leaflets. 



The upper leaves of the annual peas are composed 

 of 1-4 pairs of leaflets, which are rarely exactly opposite. 

 They are rather uniform in shape, in most species, the 

 lower leaflets the larger and the upper ones decreasing 

 in size. They, like the whole plant, are soft, succulent, 

 and more or less glaucous. The leaflets are folded or 

 plicate in the bud. The margins may be entire or 

 especially in the lower leaves, dentate. 



On the plants belonging to the subspecies arvense 

 the internodes or points of attachment of the stipules 



S. T Wellensick, Genetic monograph on Pisum (Bibliographica genetica, 2:343-476. 1925). 



