WOOD SORREL 



133 



Find a flower-stalk of wood sorrel, and look for the upper 

 organ of movement, whose place is indicated by a small 

 two-pointed bract (Fig. 33 d). Where the bract springs, 

 some species of Oxalis send out several flower-stalks, and 

 the minute bract of our common wood sorrel probably 

 marks the place where the flower-stalk once broke up into 

 several. There is also 

 a ring-like organ of 

 movement at the base 

 of the flower-stalk (Fig. 

 340). Study of the 

 movements of the 

 flower-stalk will show 

 you that it droops by 

 night or when the 

 flower is shaded, erects 

 itself in the weather 

 and light which en- 

 courage the petals to 

 expand, droops after 

 flowering, and erects 

 itself once more for 

 the ejection of the 

 seeds. 



It is easy almost any seed-coat; in. s.c., inner seed-coat; alb, 



time in Summer to See * lbumen or food-reserve of seed ; em, em- 



bryo (cotyledons). To the left is seen the 



the long-Stalked fruits integument of the seed after discharge; the 



of wood sorrel pushing elastic cuticle has now become internaK 

 through the leaves. If you gather a few and lightly press 

 them, they will perhaps go off with a faint pop, and a 

 seed or two will shoot to a distance. After all the seeds 

 are discharged, the fruit looks much the same as before, 

 for the openings close up immediately. 



There are many plants which throw out their seeds by 

 the twisting of the seed-vessel, or by the squeezing together 

 of its walls, or by the sudden release of the carpels, but 

 wood sorrel is peculiar in this, that the propulsive 



FIG. 35. Wood sorrel seed, before and 

 after discharge. To the right is seen the 

 seed in section; cut, cuticle; out. s.c., outer 



