CHAPTER 14 

 GENERAL CHARACTERISTICS OF THE LEGUMINOS^ 



This family of approximately 487 genera and 10,782 species of plants 

 is next to the grass family the most important one economically speaking 

 in the vegetable kingdom. It includes herbs (clovers), shrubs (clammy 

 locust) and trees (mesquite, honey locust). 



Roots. Their roots are both primary and secondary upon which are 

 found nodules, or tubercles, of varying size. These tubercles are in- 

 habited by a bacterium, Pseudomonas radicicola, which is active in their 

 formation. It is believed that this organism associated in the galls or 

 tubercles with the leguminous plants is capable of utilizing free atmos- 

 pheric nitrogen, and in some way is able to transform this inorganic nitrogen 

 into organic nitrogen, which is absorbed by the higher green leguminous 

 plants. 1 



Stems. The stems of the herbaceous plants of the family are annual 

 (peas), biennial (sweet clover) and perennial (alfalfa). Sometimes twining 

 stems are met with in the herbaceous stems (bean), or in the woody stems 

 (Wistaria), when they are known as lianes. Occasionally, as in the genus 

 Lalhyrus, the stems may be winged. 



Leaves. The leaves are alternate and stipulate. The stipules, as in 

 the pea, may be enlarged and leaf -like, in other cases (black locust), they 

 may be converted into spines. The leaves are simple (Ckorizema), or 

 compound, palmately, or pinnately compound. The palmately com- 

 pound leaf may be trifoliate of three leaflets, or as in lupine, there may be 

 as many as seven to eleven leaflets. The pmnately compound leaves 

 may be trifoliate with the middle leaflet provided with a longer petiolule 

 than the other two, or it may have more than three leaflets, up to many, 

 with a terminal leaflet (odd, or imparipinnate), or with a pair of terminal 

 leaflets (parip innate), or ending in a simple, or a branched, tendril 

 (tendriliform, or cirrhiferous). The bases of the leaflets and the base of 

 the common petiole have swellings known as pulvini. The presence of 

 these pulvini enables the leaflets to assume nyctitropic and hot-sun posi- 



1 See Chapter 16. 



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