242 STUDY OF COMMON PLANTS^ 



some of the cases in which such affinities are plainly marked. 

 A few of these will serve as examples of many others. 



The Cruciferse, as we have seen, are so plainly defined 

 by their cruciform, tetradynamous flowers, pungent proper- 

 Groups of ties, and characteristic fruits and seeds, that we 

 families, naturally think of them as sharply marked off 

 from all other families of plants. A number of smaller 

 families, however," are manifestly related to them. In one 

 of these, the Capparidacese or caper family, the flowers are 

 cruciform, the plants often pungent, the pods nearly the 

 same as those of the Cruciferae, and the seeds similar; but 

 there are certain differences of the embryo and stamens 

 that require a separation of the two families, which other- 

 wise are nearly identical in their characters. In like man- 

 ner the members of the Rosacese, another prominent and 

 well-marked family, show such plain affinities with the 

 Saxifragacese that the differences by which the two families 

 are distinguished from each other seem trivial in compari- 

 son with their strong likeness. Again, while the Labiata?, 

 with their square stems, opposite leaves, bilabiate flowers, 

 and aromatic properties, form a most characteristic group 

 of plants, their relationship with the Verbenacese, which 

 exhibit a number of characters in common with them, is 

 manifest at a glance. In the same way the Asclepiadacese 

 and Apocynacese show a remarkable likeness, and this is 

 still more strikingly true of the Liliaceae and a number of 

 families that form with them another marked group, or 

 order. 



These examples are sufficient to illustrate the natural 

 grouping of families into orders. Thus, the Labiatse with 

 Orders and n ^ De ther families constitute the Labiatiflorse, 

 higher groups, the Liliacese with fifteen other families the 

 Liliiflorse, and so on. At present botanists recognize some 



