206 APPENDIX 
bracts is called an involucre and if there are secondary whorls on 
the branches of the inflorescence they are called involucels. 
24. In the grasses the flowers are arranged in spikelets con-. 
sisting of an axis, the rachilla, bearing two rows of bracts. The 
lowest two are empty and are known as empty scales or glumes. 
The rest usually bear a flower in the axil and are known as flower- 
ing scales or lemmas. Between the flower and the rachilla is an- 
other bract called the palet or palea. 
25. In the composites the head is surrounded by from one to 
several series of bracts forming the involucre. Some of the com- 
posites have in addition to these, other bracts mixed with the flowers 
in the head, the florets occurring in the axil of bracts called chaff. 
26. Plants that live but a single season are annuals, those liv- 
ing two seasons are biennials, those living several to many years 
are perennials. Plants which do not form much woody tissue and 
whose stems live but a single season are herbs. Plants which form 
woody stems which persist from year to year are trees or shrubs. 
Trees differ from shrubs in being higher and having usually but a 
single stem, while shrubs are low and often have many stems. 
27. In some plants the stem is under ground and usually short. 
They thus appear stemless and are called acaulescent. In such plants 
the flower stalks come directly out of the ground and are called 
scapes. The dandelion is a common example. 
28. All measurements are given in the metric system. For the 
convenience of those not familiar with this system the following 
table of approximate equivalents will be useful: 
Metric English 
PPE TPATINCL EI = (tii yee ee RS ee ee 1% line or 1445 inch 
MBP EIGTECUCT 4 CHES oo oe eta ne Oi cee ee % inch 
1 decimeter (dm )............. Back) oh Prk BY Raia PRONE A Be Oe 4 inches (3.94 in.) 
Mere beE Miho) F.6d fay arse Pe BE | SMR pe Dy ae 40 in. (39.4 in.) 
English Metric 
UL CUST GEO 4 Se. ne TR et AE ORETE Ee SUN C RR ten PALE Te SUM eT oe8 © 2 millimeters 
Le ite lees ie ute Bap Fs ee on RO eS Wits 2.5 centimeters 
1) 1a 7g) Ree Rp ae ee ae ee See Pa. ati a. ee eS 3 decimeters 
