236 Minnesota Plant Life. 



of stamens, and five carpels, or more, fused together to make 

 the fruit-rudiment in the flower of a plant belonging to the 

 higher class. In both classes of higher seed-plants there are 

 many variations from the rule and in some plants of the highest 

 class, flowers very similar in general plan to those of the lily 

 might be observed. Yet the differences which have been 

 pointed out are fairly general and in most instances serve to 

 distinguish the proper class of a plant in question. 



The highest class, comprising over 120,000 species, is by far 

 the richest in forms of any in the vegetable kingdom. Two 

 sub-classes are recognized, in each of which are grouped a 

 number of orders. The higher sub-class comprises all those 

 forms in which the petals are normally fused together by their 

 sides to make a corolla-tube a structure of which the honey- 

 suckle, or the morning-glory affords typical examples. When, 

 however, the petals are distinct from each other or are quite 

 reduced and insignificant, the flower is regarded as typical of 

 the lower sub-class. 



Casuarina trees. The first and lo\vest order of the highest 

 class includes a curious family of trees, the casuarinas, not rep- 

 resented in North America. In appearance their branches 

 would remind one of those of the horse-tail. They are abun- 

 dant in northern Australia and the Malay archipelago, and differ 

 from most other seed-producing plants in forming more than 

 one large-spore in the ovule, so that in a single seed more than 

 one female plant may arise. Another odd habit of the casu- 

 arinas which appears, however, in some of the other families 

 of the class is the penetration of the seed-rudiment by the 

 pollen-tube, not through a canal at its tip, as is the rule, but 

 through a cleft in the base. Therefore the seed-rudiment, which, 

 it must be remembered, is equivalent to a spore-case in the 

 ferns, may be regarded, in these plants, as splitting open and 

 partially exposing the spores inside a behavior recalling very 

 strikingly the ordinary opening of spore-cases in lower forms. 



Lizard's-tails and peppers. The second order includes four 

 families of which the pepper family is the most important. 

 Here belong the peppers and cubebs from which spices are 

 obtained. They are nearly all tropical and none of them occur 

 in Minnesota. 



