ANGIOSPERMS. 195 



if they have just opened observe the great quantity of yellow "dust." 

 These are the pollen grains, or the small spores. (The anther sacs Ihen must 

 be the small sporangia.) 



320. The inner whorl (gynoecium). — Note that the structure in the centre 

 of the trillium flower ends in three slender points ; cut across the larger 

 part of this object below. Nole that it has three chambers. What does this 

 suggest? What do you find attached to the inner walls of these chambers ? 

 They are the ovules. Sketch a cross-section. Is there any relation be- 

 tween the three parts of this structure (pistil) and leaves ? What is this 

 relation ? Compare the mature fruit of trillium (if at hand) with the pistil 

 and ovules. 



Description of Trillium. 



321. General appearance. — As one of the plants to illustrate 

 this group we may take the wake-robin, as it is sometimes 

 called, or trillium. There are several species of this genus in 

 the United States; the commonest one in the eastern part is 

 the " white wake-robin " (Trillium grandiflorum). This occurs 

 in or near the woods. A picture of the plant is shown in fig. 

 175. There is a thick, fleshy, underground stem, or rhizome 

 as it is usually called. This rhizome is perennial, and is marked 

 by ridges and scars. The roots are quite stout and possess 

 coarse wrinkles. From the growing end of the rhizome each 

 year the leafy, flowering stem arises. This is 20-30 cm. (8-12 

 inches) in height. Near the upper end is a whorl of three ovate 

 leaves, and from the centre of this rosette rises the flower stalk, 

 bearing the flower at its summit. 



322. Parts of the flower. Calyx. — Now if we examine the 

 flower we shall see that there are several leaf-like structures. 

 These are arranged also in threes just as are the leaves. First 

 there is a whorl of three, pointed, lanceolate, green, leaf-like 

 members, which make up the calyx in the higher plants, and the 

 parts of the calyx are sepals, that is, each leaf-like member is a 

 sepal. But while the sepals are part of the flower, so called, 

 we easily recognize them as belonging to the leaf series. 



323. Corolla. — Next above the calyx is a whorl of white or 

 pinkish members, in Trillium grandiflorum, which are also leaf- 



