RUDIMENTS OP BOTANY. XVH 



113. The pistil is either the modification of a single leaf, or of one 

 or more whorls of modified leaves ; the latter being termed carpels. 



114. When the margins of the folded leaf out of which the carpel is 

 formed meet and unite, a copious developement of cellular tissue takes 

 place, forming what is called the 'placenta. 



115. If no union takes place among the carpels, the ovary is termed 

 apocarpous, as in Ranunculus ; but if there is an adherence, so that a 

 compound ovary is formed, it is called syncarpous. 



116. When carpels unite, those parts of their sides which are con- 

 tiguous grow together, and form partitions between the cavities of the 

 carpels, called dissepiments. 



117. When these dissepiments are so contracted as not to separate 

 the cavity into a number of distinct cells, but merely project into a 

 cavity, the placentas which occupy the edges of these dissepiments be- 

 come what is termed parietal. 



118. If the dissepiments are abortive or obliterated, the placente re- 

 maining unaltered in the axis, a free central placenta is formed. 



119. A one-celled ovary may also be formed out of several carpels 

 in consequence o.f the obliteration of the dissepiments ; Ex. Nut. 



120. If the ovary adheres to the sides of the calyx it is called inferior, 

 and the calyx is said to be superior. 



121. If it contracts no adhesion with the sides of the calyx, it is 

 called superior, and the calyx inferior. 



122. The ovule or ovulum is a body borne by the placenta, and is 

 destined to become the seed ; its position is of great importance in de- 

 termining natural affinities. 



123. When the ovule is fixed by its base to the bottom of one of the 

 cells of the ovary, of which it takes the direction, it is said to be erect ; 

 or if it hangs from the summit of the cell, it is inverted. 



124. When it is attached to the middle portion of the placenta, it 

 may have an upright direction, and is then called ascendant, or point 

 downwards and is then suspended. Generally, however, the erect and 

 ascendant ovule are confounded under one name, and the inverted and 

 suspended are known by the term pendulous. 



125. The ovule is either sessile, or on a stalk called thefuniculus or 

 podosperm ; and in either case the point by which the union is formed 

 is termed the base of the ovule, and the other extremity the apex. 



126. The ovule consists of a nucleus and two external coats ; the 

 outer of which is called the testa-or primine sac ; and the inner, the in- 

 ternal membrane, or secundine sac, or the tegmen. 



127. The base of the nucleus is always incorporated with the base of 

 the internal membrane, and their common base is attached at some 

 points to the testa. The junction of the three, forms the chalaza. 



128. The mouths of the primine and secundine sacs usually con- 

 tract into a small aperture called the foramen of the ovule, or the exos- 

 tome. It is through this foramen that the molecules of the pollen are 

 introduced into the nucleus ; and its position indicates the future posi- 

 tion of the radicle of the embryo, the radicle being always next the 

 foramen. 



