DEVELOPMENT OF LEAF-OEGA]S T S. 60 1 



Corolla. The petals usually originate after the sepals in successive 

 spires, or, much more commonly, in simultaneous whorls. In the case of 

 g-amosepalous or gamopetalous flowers, the sepaline or petaline tubercles 

 usually originate free and from above downwards, being afterwards raised 

 from below by the growth of the tube. The tube then, in such cases, does not 

 consist of coherent parts, as is sometimes stated, but of parts partially 

 arrested in their development, and consequently not separated. In other 

 cases, especially in the carpellary whorl, the tubular portion is thrust out 

 from the axis prior to the formation of tubercles on its free edge. 



Stamens. These originate either spirally or in whorls, usually from 

 below upwards, or from circumference to centre; if verticillate they 

 always appear simultaneously. According to Payer, the stamens split 

 like the sepals in the | arrangement ; and this certainly occurs in the case 

 of some polyandrous flowers, e.g. Polygomim. Where there are two 

 whorls, generally the outer, but at other times the inner, is developed 

 first. 



Compound stamens, or phalanges of stamens, originate as simple tuber- 

 cles, from the sides of which spring the secondary staminal tubercles 

 from above downwards, as in Mallows. Sometimes one or more lobes or 

 (staminodes) are antherless and petaloid : thus in some cases we have an 

 arrangement like that of an imparipinnate leaf, the terminal lobe peta- 

 loid, the lateral ones antheriferous. The whole course of development 

 in such cases precisely resembles that which takes place in the compound 

 leaves of some Passion-flowers or of the Rose. 



Gyncedum. The carpels are developed after the stamens from small 

 tubercles, at first free, but afterwards (in syncarpous ovaries) becoming 

 coherent. The original tubercle is more or less spheroid ; but as growth 

 goes on, the marginal portions grow more rapidly than the central por- 

 tion, as in the case of a conduplicate leaf, so that a groove is formed. In 

 due time the margins unite, and thus the cavity of the ovary of an apo- 

 carpous pistil is formed ; the ovary in a syncarpous pistil is formed by the 

 blending of the margins of adjacent carpels. The styles are formed from 

 the lengthening of the apex of the ovary from below upwards. In the 

 case of inferior ovaries the thalamus, instead of remaining more or less 

 convex, becomes concave and cup-shaped by the greater proportionate 

 growth at its circumference. The carpels originating from this receptacle 

 become thus more or less completely concealed within, and sometimes 

 adherent to it. In some syncarpous pistils, like the Primrose, the carpels 

 originate as a ring or shallow tube, from whose free border the tubercles, 

 which elongate into the styles and upper part of the carpels, are de- 

 veloped. 



Ovules. The ovule arises from the placenta as a cellular papilla, the 

 nucleus (fig. 601). Around the base of this is formed a ring, which gra- 

 dually lengthens from the base upward into a tubular sheath or coat of 

 the ovule, b. The succeeding coats, which vary in number in different 

 plants, are formed in like manner, are wholly cellular in the first instance, 

 and sometimes permanently. They leave at" the apex an unclosed portion 

 or hole, the micropyle. During the growth of the coats of the ovule a 

 change in direction usually occurs, so that the ovule becomes inverted. 



The true nature of the ovule and its origin are still matters of contro- 

 versy. Hofmeister considered that they arise like hairs from the epi- 



