H4 BOTANY 



from the rest as the sporophylls. They are usually 

 considered to be modified leaves, as the name indicates. 

 The outer whorl consists of bodies very unlike leaves in 

 appearance. Each shows a slender stalk or filament 

 bearing at its top a swollen head or anther. The whole 

 club-shaped organ is called a stamen. Each anther 

 contains a group of four chambers, which are the 

 sporangia, and inside them are the small spores. They 

 are commonly spoken of as pollen sacs, containing pollen 

 grains. These were the old names applied to them 

 before their true nature was understood, and they are 

 retained still as a matter of convenience. 



Like the sepals and petals the stamens may be joined 

 together in various ways, or they may be free. They 

 may grow from the flower stalk, or they may appear to 

 spring from the calyx or the corolla. These appearances 

 are due to curious irregularities in the growth of the 

 parts of the flower. 



The sporophylls of the final whorl are known as 

 carpels, and together they form the pistil. In shape the 

 carpels resemble a leaf folded on the mid-rib till the 

 edges meet and become united, so that a cavity is 

 formed inside them. This cavity is the ovary. It is 

 more usual to find the carpels united by their edges to 

 form a large ovary, which is often divided up into several 

 chambers. The sporangia are found in the interior of 

 the ovary, attached usually to the edges of the carpels. 

 They were formerly called ovules, and the name is still 

 often used (Fig. 46) . The ovule or mega-sporangium is a 

 fairly substantial structure. As the spore never leaves 

 it but produces its prothallus in its own interior while 

 still within it, and as the young embryo plant is developed 

 on the prothallus inside the spore, it is clearly an organ 

 of the greatest importance. It consists of a mass of 

 small cells called the nucellus, and is covered by two 

 membranes or integuments which also are many-layered 



