306 



CASSELL'S POPULAR GAPDEXING. 



There are certain points in the rix^ening- of fruits, 

 well known to practical men, hut which have not 

 as yet received from hotanists the attention they 

 deserve. Thus the paaturation of Peaches and 

 Grapes, for instance, is not marked hy one con- 

 tinuous increase in size, but there is as it were a 

 cheek for some weeks during- the " stoning period." 

 Then occurs the " second swelling," which goes on 

 uninterruptedly if circumstances be propitious. The 

 explanation given by gardeners is that the increase 

 in size is temporarily arrested during the develop- 

 ment of the stone, in the case of stone fruit, or the 

 formation of the hard seed in the Vine, and that 

 once these latter processes are satisfactorily accom- 

 plished the second swelling occurs. The facts arc 

 beyond dispute, but the explanation given has not 

 as yet been accurately tested ; at any rate, practi- 

 cally it is well known that if the fruits be over- 

 stimulated during the stoning period, they resent 

 the interference, and either fall off, as in the Peach, 

 or the fruit suffers in quality, as in the Vine. 



Physiologically the ripening of the fruit consists 

 in the transport or formation of various juices and 

 their manifold chemical transformations. Let us 

 take the Grape as an example. The young ovary 

 is of small size, green, soft, tasteless, or faintly 

 acid; after fertilisation it swells, its constituent 

 cells multiply, the watery juice accmnulates, the 

 acidity increases, tannin is deposited in the skin 

 and in the seed. All the time the young fruit 

 remains green, the work it has to do is the same 

 in kind as that effected by the leaf ; hence to gain 

 an idea of w^hat the green fruits do, and what are 

 the conditions most propitious for the purpose, the 

 reader should refer to the account given of the 

 mode of growth and action of the leaf when 

 exposed more or less to the light. But as ripening- 

 advances under the influences of increasing tem- 

 perature, or what comes to the same thing, of 

 the prolonged exposure to an equable temperature, 

 Ihe green colour gradually gives place to the colour 

 peculiar to the particular fruit, the sour acids 

 disappear, sugar is developed, and slowly but 

 surely the whole composition of the fruit alters. 

 Unripe fruits contain a large proportion of water, 

 and a notable quantity of gummy substance called 

 pcctose, which undergoes various chemical changes 

 during the process of ripening, and which is the 

 source of the jelly-like substance so familiar to 

 us in " Currant jelly." 



The favourite culinary mixture of Currants and 

 Raspberries finds its explanation in the presence of 

 this ferment, " pectose," which acts on the "j)ectin" 

 of the Currant, and transforms it into an acid jelly. 

 M. Buignet has determined the average amount of 

 acid per cent, in various descriptions of fruit, and 



from ms tables, as cited by M. Deherain, we 

 extract the following : — 





Acid per cent. 



Sugar per cf 



Peuclies, uuripe 



3*9 



5'9 



Peaches, ripe 



07 



'. 1-9 



Grapes, unriije 



2-4 



1-6 



Grapes, ripe . 



0-3 



. 18-3 



Apricots . 



1-8 



87 



White Currants 



1-5 



6-4 



Raspberries 



13 



7'2 



Greengages 



1-2 



5-.5 







. 13-9 



Cherries . 



0-6 



. lO-O 



Strawberries . 



0-5 



. 11 3 



Pine-apples 



3-5 



. 13-3 



Pears 



0-8 



7-8 



Figs 



. 0-05 



. 11-5 



These figures will suffice for pm-poses of general 

 illustration; it will, of course, be understood that 

 the amoimts will vary according- to sort, season, and 

 stage of ripeness ; notwithstanding the proportions 

 will remain nearly the same. M. Buignet has also 

 studied, comparatively, several kinds of .Strawberries, 

 from a chemical point of view. Princess Royal and 

 Elton are types of a group of Strawberries remark- 

 able for abundance of juice and acid, and a small 

 proportion of sugar. The Alpine Strawberries are 

 much more sugary, not very juicy, and slightly 

 acid; while the Hautbois" are ver}^ slightly jiiicy. 

 with little acid, and a large proportion of sugar. 



In general terms it may be stated that fruits 

 pass through three stages. In the first, which is 

 that of devcloj)ment, the fruit is green, and docs the 

 work of a leaf. 



In the second period, which is that of matura- 

 tion, the colour changes ; it no longer emits oxygen 

 gas when exposed to the light, but gives off carbonic- 

 acid. During this period a series of changes (com- 

 bustions the chemists caU them) occurs, in conse- 

 quence of which the tannin disappears first, followed 

 by the acid, and, after a time, by the sugar also, 

 when the fruit becomes insipid. 



The third stage is one of decomposition, the effect 

 of which is to set the seed at liberty, by the rotting- 

 of the fruit. Air enters the cells of the fruit, its 

 sugar is converted into alcohol through the agency 

 of the infinitesimally minute spores of a fungus, 

 which acts like yeast, carbonic acid being given 

 off; while the alcohol, acted on by the remaining 

 acids of the fruit, forms various ethers, to which 

 the fruits owe their fragrance. Finally, the air 

 destroys the cell- walls, " blets " them, and at the 

 same time destroys whatever acid or tannin material 

 may be still left ; thus the acid astringency of the 

 Medlar, of the Persimmon {Djospijros) , which renders 

 the young fruits uneatable, is removed by the- 

 process of blotting. 



The changes above referred to are, in general, the 

 dii-ect consequences of fertilisation ; but in some 

 cases it happens that the fruit ripens, and even the 



