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 i fthere 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. 



30. 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 milimetre (mm.) one-half line 



1 centimetre (cm.) two-fifths inch 



1 decimetre (dm.) four inches (3.94) 



1 metre (m.) 3 feet 3.37 inches 



English. Metric. 



1 line 2 millimetres 



1 inch 2.5 centimetres 



1 foot 3 decimetres 



