ORGANS OF EEPRODUCTION. 



295 



Fig. 640. 



special manner (as already mentioned nnder the head of the 

 Peduncle) (see page 194), to indicate this body, when it is 

 shortened and dilated in a more or less horizontal manner, and 

 bears a number of flowers ; Avhile the term torus is also used by 

 some botanists, as synonymous with disk. (See page 265.) To 

 prevent confusion, therefore, it Avould be far better to apply the 

 term thalamus alone, to the apex of the peduncle or floral axis 

 upon which the different whorls of a solitary flower are arranged. 

 This term has been therefore chiefly used in this volume. 



In the majority of plants, the thalamus is a httle flattened 

 surface or point, and accordingly presents nothing remarkable; 

 in other plants, however, it becomes much enlarged, and then 

 assumes a variety of appearances, and thus modifies to a con- 

 siderable extent the form of the flower. Most of these forms 

 have been already referred to when 

 describing the pistil, but it will be 

 more convenient for reference, &c., 

 if we now speak of all the essential 

 modiflcations. In the Magnolia, 

 Tulip Tree, and plants of the order 

 Magnoliaceae generally, the thalamus 

 is cyhndrical {jig. 589); in the 

 Pine-apple also (fig. 706, 2), and 

 plants of the order Anonacese gene- 

 rally, it acquires a somewhat similar 

 form; in the Raspberry {fig. 591), 

 Ranunculus {fig. 530), and Adonis 

 {fig. 592), it is conical ; in the 

 Strawberry {fig. 590), it is hemi- 

 spherical ; in Nelumhium {fig. 640), 

 it is a large tabular expansion, in which there are a number of 

 cavities containing the ovaries. In the Rose, it forms a concavity 

 upon which the carpels are placed {fig. 439). 



In the Primulacese, Santalaceae, and in all cases where the 

 placenta is free from the walls of the ovary from its earhest 

 appearance, the thalamus becomes prolonged into the cavity of 

 the ovary and forms the placenta. At other times the thalamus 

 becomes prolonged beyond the ovary, as in the Geraniaceae, 

 UmbeUiferffi, &c. ; this prolongation is termed a carpophore. In 

 the Geranium {fig. 626), this carpophore forms a long beak- 

 hke process, to which the styles are attached, and which only 

 separate when the fruit is ripe. In some cultivated flowers, as 

 in the Rose, the thalamus will frequently acquire a monstrous 

 development, and become extended into a branch bearing true 

 leaves instead of carpels {fig. 641). 



In some plants the thalamus becomes prolonged beyond the 

 calyx and forms a stalk to the ovary, to which the term of 

 gynophore has been applied. (See p. 281.) This may be seen in 

 U4 



Fig. 640. Thai. Thalamus of Ne- 

 lumhium. carp. Carpels. 



