268 THE SEED PLANTS : FORMS AND LIFE- HISTORIES 



Rhizomes. 



(2) Examine and sketch a portion of the Couchgrass or 

 " Twitch " {Agropyrum repens) or any grass of similar habit. 

 The main stem of the plant is the rhizome, bearing scale leaves 

 and roots. The aerial leafy shoots arise from buds in the axils 

 of the rhizome scales. Branching of the rhizome is secured by 

 the outgrowth of other axillary buds which grow horizontally. 

 Note the abundant production of roots at the bases of the aerial 

 shoots, and the sharp points formed by the folded scales covering 

 the terminal buds of the rhizome branches. These can penetrate 

 stiff clay and often bore through objects such as potatoes which 

 they may encounter. 



(3) Compare the stout, more slowly growing rhizome of Solo- 

 mon's Seal (Polygonatum). The scales which cover the terminal 

 bud fall off, leaving only brown circular scale scars on the surface 

 of the rhizome. The single aerial shoot is formed each year by 

 the turning up of the terminal bud. The continuation and 

 branching of the rhizome are secured by other buds formed in 

 the spring. Compare the early spring condition with the summer 

 condition (museum or herbarium specimens) . 



Tubers. 



(4) Sketch the tuberously thickened branching rhizomes 

 of the Chinese Artichoke {Stachys tuberifera). Note the thin 

 portions of rhizome preceding and following the tubers, the 

 constricted nodes, with triangular scales and axillary buds in 

 opposite pairs, alternating on succeeding nodes, and the up- 

 wardly turned terminal bud. 



{5) Examine potato tubers — a seed potato ready for planting, 

 and a sprouted potato are most instructive. Mark on your 

 drawings the scar of the tuber stalk, the eyes, the terminal bud, 

 and in the sprouts the scale leaves, developing foliage leaves and 

 adventitious roots. Examine a specimen showing early stages 

 in the formation of tubers with the stalk arising from the axil of 

 a leaf on the parent plant and the minute scales on the very 

 young tuber. 



Corm. 



(6) Crocus, autumn stage. Carefully peel off the dry mem- 

 branous scales and note that they are inserted one above the 

 other, the lower ones overlapping the upper on the side of the 

 corm, leaving brown circular scars when detached. Identify 

 the stem scars at the top and bottom of the corm. The former 

 is the scar of last spring's flowering and leafy shoot, of which 



