OliGANS AND SYSTEMS OF ORGANS. 163 



hract.9, are above the foliage-leaves and below the flowers. They 

 are nsiially of a more simple structure than the true leaves; the 

 petiole is wanting, ifsually the sheath and blade are 7iot differ- 

 entiated. They function as organs of protection for the young 

 flower, as is well illustrated in the hracts of the genus Allium and in 

 orcliids, in the iiivolucre of Couij)ositce, ghimes of grasses, etc. The 

 development and position of hypsophyllary leaves are based upon 

 physiological and anatomical (teleological) requirements, and is not 

 merely accidental. They occur most frequently in |)lants without a 

 calyx, since they supplant the function of that organ. 



5. Floral leaves. The peduncle terminates in the receptacle 

 which bears the foral leaves. Their function is to aid in the proc- 

 esses of reproduction either directly or indirectly. By the term 

 flower is understood a complex organ, a bud developed into sexual 

 reproductive organs (Eichler). A flower is a modifled branch. 

 In the. infloresctnce we therefore have to do with a branching por- 

 tion of a stem. 



We shall consider the flower with its various so-called leaf-modi- 

 iications, as calyx, corolla, stamens, and pistils, in Part lY (repro- 

 duction) in order to avoid needless repetition, especiall" as function 

 is considered to be of prime importance. 



In conclusion we shall add a few remarks on the coloring in the 

 various leaf-modifications. The green color of foliage-leaves is of 

 functional importance (assimilation) ; likewise the variegated color- 

 ing of floral leaves (fertilization by means of insects). The hypso- 

 phyllary leaves ujay be colored to perform the function of a foliage- 

 leaf or of a floral leaf, or of both ; likewise the calyx, though it is 

 usually green. The cataphyllary leaves are rarely green; sometimes 

 they are variously tinted, though the colors are usually not brilliant ; 

 often they are white. 



Critical Observations on the Distinction of Organs. 



As already stated, the term " organ " is a physiological concep- 

 tion. Yet it is customary to classify organs upon a Diorpfiological 

 basis, especially according to the morphology of development. In 

 such a procedure great care is necessary in order to avoid mistaken 

 conclusions. If we consider the thallome, leaf, stem, root, and 

 trichome as the five chief organs of plants, it will not be found 

 difficult to add the organs of reproduction (since they originate in 



