HOW FRUITS ARE MADE. 



609 



In other cases " pseudocarps " may be formed without any pollination, 

 and even without there being any flower at all. 



In many instances the ovaries are invested by a receptacular tube, i.e. 

 " inferior " ovaries, as they are called ; since this is of the nature of an 

 axis, it may swell into a fruit-like body, even when the flower within it 

 has been totally arrested. 



This occurs in Pears, as the "Bishop's Thumb," and in the not un- 

 common condition of " pears on pears," as it might be called. In these 

 several internodes of a branch swell into " pears " one above the other, 

 there being no trace of a flower at all. 



This method may account for some seedless Cucumbers and Bananas, 

 both being " inferior" fruits. 



Fkuits of a Single Carpel. — To see how fruits of complicated 

 structures arise from more simple conditions, it will be as well to begin 

 with those having a single carpel only, like the familiar pea-pod. 



A carpel is really an altered leaf. We must imagine the two halves 

 of the leaf -blade to be folded together, as is so frequently the condition 

 of young leaves when escaping from buds in spring. The margins are 

 greatly thickened, as they have to carry and nourish the ovules. They are 

 then called the "placentas." Fibro-vascular bundles now pass up them, 

 sending off a little branch to each ovule. These vascular cords are 

 wanting in an ordinary leaf. Then the lower part swells into a bag-like 

 structure called the "ovary," which encloses the ovules, forming two 

 rows along the two cohering margins. The upper part is drawn out into 

 the style, the apex of which, having no skin or epidermis, is composed of 

 projecting cells which catch and retain the grains of pollen. Such is the 

 origin of the pea-pod. 



The pollen-grains send down long tubes which enter the ovules and 

 convey fertilising matters, by means of which an embryo is formed in 

 each ovule.* As the embryo is formed, so the carpel grows and becomes 

 the pod, the ovules becoming the peas or seeds. 



When perfectly ripe the pods burst by contracting on drying up. 



There are two ways in which such pods burst or dehisce. The pea- 

 pod, called a " legume," splits down both edges into two halves, often 

 curling up so that the seeds are scattered to a distance. The edge 

 bearing the peas is called the "ventral suture," the other is the "dorsal 

 suture," as it corresponds to the midrib of the carpellary leaf. 



If the pod burst down one edge only, it is called a "follicle." This 

 usually bursts by the ventral suture, as in Larkspur and Aconite ; but 

 in Magnolias, in which the pistil is composed of a dense mass of almost 

 woody follicles, the seeds could not escape by the ventral, so Nature lets 

 them out by the back door, or dorsal suture, instead. 



If a pod contain only one seed, it generally becomes a tight-fitting 

 covering to it, and is consequently indehiscent. This occurs in the Sain- 

 foin. It is then the same thing as the achene. Familiar examples of 

 this are the fruits of the Buttercup, Strawberry, and the achenes inside 

 the hip of the Rose. Sometimes a legume forms a string of indehiscent 

 parts investing each seed, being strongly constricted between them. It 



* It is unnecessary to enter into minuter details of the process on this occasion. 



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