286 PHITUM XIV. ANTHOPHYTA 



cup (''receptacular cup")- In such a typical flower 

 as a Buttercup (Ranunculus) this axis is globular. 



517. In the Buttercup the globular axis is spirally 

 studded with many carpels (simple pistils) each consisting 

 of a closed cavity below (ovar}'), gradually tapering 



above to the soft terminal part (stigma). 



When young the carpel (megasporophyll) 



is an open, flattish, leaf-like structure, but 

 vert'i^ai pian'^ as it grows larger its margins curve up- 

 flowrr"''"''^''' ^vard until they meet and grow together. 



While the carpel is closing, an ovule grows 

 out from the base, and becomes enclosed by the carpel 

 walls. 



518. Below the globular head of carpels (pistils) are 

 several rows of stamens spirally encircling the axis. Each 

 stamen is a stalked, somewhat flattish structure (micro- 

 sporophyll), bearing four elongated, parallel sporangia 

 which contain microspores (pollen). Commonly the 

 stalk is called the filament, and the four sporangia to- 

 gether, the anther. The sporangia (pollen sacs) split 

 longitudinally at maturity and permit the escape of the 

 pollen. 



519. Still lower on the flower axis are two series of 

 leaf-like structures also spirally arranged, constituting 

 the perianth. The upper series includes five rounded, 

 yellow petals, the whole being known as the corolla. 

 The lower series is made up of five pointed, green sepals, 

 this being known as the calyx. 



520. The purpose of a flower is the production of 

 seed, and in the Buttercup this is accomplished as 

 follows: 



521. In the ovule (megasporangium) an axial spore 

 mother cell (archespore) arises, and later this divides 

 into four young cells (megaspores), but only the deeper 



