Ad CLASS-BOOK OF BOTANY. 
and the silky surfaces. The small flowers are crowded into 
globular heads placed on long penduncles. Get them, if 
possible, at all stages of development. In flowers just opened 
note the 4-angled and 4-lobed calyx, which is generally 
covered with bristle-like hairs, while from each angle there 
Fig. 60. Flower of Acena, in Fig. 61. Spine of calyx 
longitudinal section. of Acena. 
rises a stiff green spine with several barb-like reversed hairs 
at its apex. The calyx-tube is applied so closely to the ovary 
as to appear almost adnate to it, while attached to its upper 
portion are the 4 petals, which are slightly united at the base 
toform a 4-lobed imbricate corolla. The stamens are usually 
3 or 4 in number, sometimes fewer, sometimes more, on rather 
long slender filaments. The ovary contains 1 pendulous ovule, 
and bears a flattened plumose stigma. When nearly mature the 
ovary will be found to have ripened into an elongated achene, 
closely enclosed in the hardened calyx-tube, and having its 
spines also elongated and hardened, forming the well-known 
appendages or burrs, by means of which the seeds are dis- 
tributed. 
(¢.) The Apple (Pyrus malus) presents a modification of the rose- 
structure. First, note that the leaves are simple, and furnished with 
free deciduous stipules. The chief difference, however, is in the fruit. 
In this the adnate calyx-tube (with which is probably united the enlarged 
receptacle, as in the rose) becomes succulent, forming the edible portion 
of the fruit, and enclosing the 5-celled ovary, while the withered re- 
mains of the 5 calyx-lobes remain persistent on its summit. This form 
of fruit (pseudocarp) is called a pome.}+ (In the apple the pericarp fee 
core) is horny or cartilaginous; only membranous in the pear: while in 
Hawthorn it is almost bony.) Compare with the foregoing Quince, 
Medlar, and Cydonia japonica. 
+ Lat. pomen, an apple. 
