80 



ANALYTICAL CLASS-BOOK OF BOTANT. 



to thia special purpose. This is a species of Tipula.. It 

 enters the flower, and descends to the base, where the 

 stamens and pistils seem like complete fixtures, the an- 

 thers being placed quite under the stigma ; so that, in 

 the ordinary course of things, there could be no communi- 

 cation between them. But the fly, in attempting to 

 return, is beset by inverted hairs, which thickly cover 

 the inside of the tube. Thus imprisoned, he continually 

 struggles to escape, and by this means, ajjparently so 

 simple and natural, he effectually breaks the ice between 

 the parties most interested. Fertilization ensues, the 

 flower withers, and the fly regains its liberty. It is not 

 the least curious part of this history, that an American 

 species, cultivated in England, was seldom fertilized, 

 probably for want of the good little Grenius it would have 

 found in its native habitat. 



CHAPTER XXVIII. 



THE OVAET. 



454. This organ is either simple or compound : 

 simple, when composed throughout of but one piece or 

 part ; and compound, when consisting of more than one. 

 A compound ovary is a whorl of transformed leaves, 

 with their cohering edges united in the axis, and their 

 confluent sides radiating from the centre, as may be seen 

 in the transverse section of fruit from the Lily, fig. 8, 

 Plate XXVI. 



455. Parts op the Ovary. — The divisions of a 

 compound ovary are called Carpels. The walls or par- 

 titions of these are Dissepiments, and the spaces between 

 them are Cells. In fig. 7 is seen a transverse section 

 of the compound ovary of Meadow Saffron. The dissep- 

 iments, with their double walls, and the ovules attached 

 to their inner portions, are well delineated. 



456. In the normal structure, the number of carpels, 

 dissepiments, and cells, will be equal ; but sometimes the 

 dissepiments become partially or wholly absorbed in the 

 growth, or obliterated by abortion ; while the carpels, 

 or actual parts of which the ovary is composed, remain 

 unchanged. In the diagram, fig. 1, is represented a five- 

 carpelled ovary, with its ovules, o, attached to the floral 

 axis in the centre. This is better seen in the fruit of 

 the Lily, fig. 8, which is a three-carpelled ovary, with the 

 seeds attached in the same manner. In the diagram. 



General subject Vhen is the Ovary simple— whun compound t Name 

 the divisions of a Compound Ovary — tlie walls, or partitions— the spaces be- 

 tween. How in the normal structure ? What elTect has abortion ? Several 

 deirrees of abortion in the disscpiiuents. Describe each. Do styles and stigmas 

 of a compound ovary often unite in one! Of what Is each Carpel composed- 



fig. 2, the dissepiments are only extended a little way 

 beyond the middle ; in fig. 3 they are wholly obliterated, 

 the ovules still being attached to the central axis ; in fig. 

 4, the dissepiments are the same, while the ovules are 

 attached to their first rudiments on the outside wall of 

 the ovary. Sometimes, but rarely, the styles — and more 

 rarely still, the stigmas — of a compound ovary, unite, 

 and form apparently one. 



457. It should be understood that each carpel is 

 composed of a single leaf, folded with its confluent edges 

 turned inward toward the floral axis. This may be often 

 seen in the Double-flowering Cherry, where the carpellary 

 leaves, which by culture are retransformed into petals, 

 are obvious in their folded form, being often tipped with 

 the rudiments of the stigma, and presenting other indica- 

 tions which mark their character, especially when they 

 assume the texture, color, and indentations of the proper 

 leaf, as if making an effort to return to their normal 

 shape, though growing in the midst of a flower. Two 

 such leaves are seen in fig. 15. 



458. Sutures. — The line formed by the cohering 

 edges of the infolded carpellary leaf is called the Ven- 

 tral Suture. It is always turned toward the floral 

 axis, or centre of the flower, and is a true suture, or 

 seam, as its name imports. The line opposite, in the 

 external walls of the ovary, is called the Dorsal Suture. 

 It is sometimes marked by a prominent line or ridge, and 

 is the mid-vein of the transformed leaf. In the fruit of 

 the Iris, fig. 14, the prominent line seen in front of the 

 middle section is the ventral suture; while the dorsal 

 suture bounds the side carpels, right and left. 



459. The Placenta is that part of the ovary to 

 which the ovules are attached ; and, in its normal state, 

 is a cellular outgrowth of the ventral suture. It often 

 appears a distinct cord, as in the Bean, where, in common 

 language, it is that part which is called the " string,^'' 

 and is pulled off, in preparing for the table the green pods 

 known as " string-heans.^' The pod, you will remem- 

 ber, is an ovary ; the young beans are the ovules ; the 

 cords to which they are attached, are the placentae ; and 

 the parts into which it spontaneously separates, are 

 valves. The double character of the folded leaf which 

 makes the carpel, is well shown in this structure, and 

 also in that of the Pea, fig. 1 8, where the ovules are seen 

 occupying alternate positions of the Placentse, which 

 mark the ventral suture, and also the two plates, or 

 valves, into which the pod separates. 



in what flower seen? Describe. What are /S'«i«res— the Ventral— the Dor- 

 sal? Where is the flrst always turned — at what part of the leaf? What marks 

 the second? Define Placenta— how in the Bean? Define the parts in ttie 

 fruit of the Pea. 



