202 APPENDIX 
25. The leaves accompanying the inflorescence are often quite 
different from the ordinary foliage leaves both in form and size. 
Such modified leaves are called bracts. A whorl of bracts is called 
an involucre, or if there are secondary whorls on the branches of the 
inflorescence these are called involucels. 
26. In the grasses the flowers are arranged in spikelets consist- 
ing 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 flowering 
scales or lemmas. Between the flower and the rachilla is another 
bract called the palet or palea. 
27. 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, each floret occurring in the axil of a bract. 
These bracts are called chaff. They occur in the sunflower. 
28. Plants that live but a single season are annuals, those living 
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. 
29. 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. 
380. 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. 
1 millimetre: GmM:) ¥ sicieiwcaea se one-half line 
A centimetre (Ct) .vscn tea van vend two-fifths inch 
1 decimetre Gm.) sseacearxccewnsecs four inches (3.94) 
Lo MOtre: (GMs) s2 cere ead ee nemauna ane 8 feet 3.37 inches 
English. Metric. 
A UIE > face acantniat nctcitap eae Seat pans amigos 2 millimetres 
ASIN Bie sce snctnnsiy eteanidadey x yaseuberatees anne 2.5 centimetres 
LPOOt. seuuiok scam eenhawawmden eed 3 decimetres 
