192 THE ELEMENTS OF VEGETABLE HISTOLOGY 



1. Bract tissues, 



2. Calyx tissues, 



3. Corolla tissues, 



4. Stamen tissues, 



5. Pistil tissues, 



6. Stem tissues. 



CHARACTERS OF THE FLORAL TISSUES 



Bract Tissues. These structures, which are known 

 collectively as the epicalyx, are not a part of the flower 

 as they do not originate from the torus, or structure 

 which gives rise to the floral organs. The bracts 

 originate from the stem and are foliage leaves which, 

 because of modification in form and contiguity of 

 position, simulate floral parts. Their histological 

 characters are similar to those of leaves, and they 

 show epidermal tissues with stomata and perhaps 

 trichomes, palisade layers, mesophyll and the fibro- 

 vascular structures of leaves. 



Calyx Tissues. The sepals, or calyx divisions, 

 are classed as floral organs because they originate 

 from the torus. In most flowers the sepals are green 

 and leaf-like; but in those flowers in which the corolla 

 is wanting (monochlamydeous), the calyx may simu- 

 late a corolla in appearance and structure. The 

 histological elements present in sepals include epi- 

 dermal tissues, mesophyll and simple forms of fibro- 

 vascular bundles. The epidermis (Plate 64) bears 

 stomata on the outer or free surface and may also 

 show trichomes. The green tissues consist of loosely 

 arranged mesophyll or leaf parenchyma cells contain- 

 ing chlorophyll. The palisade layers are usually 

 lacking. The fibro-vascular tissues are not as wide- 

 spread nor as complex as those of leaves; and the 

 fibrous elements are much reduced in amount. 



