368 



CASSELL'S POPULAR GARDENING. 



"we 

 in the fact that 



change, so long as sufficient nutriment were afiorded 

 and so long as circumstances remained unaltered. 

 In point of fact such relative stagnation often does 

 occur. We see commonly the "mould" or spawn 

 of a fungus maintaining its existence for very 

 long periods, but not developing into any other 

 stage of growth. So among higher plants 

 have illustrations of the same thin] 

 we may grow certain plants 

 in our stoves year after year 

 without inducing them to 

 flower or materially to alter 

 their character. Change the 

 conditions, supply a little 

 more heat, a little less water 

 at particular seasons, a fuller 

 exposure to light, and the 

 heretofore sluggish plant 

 wakes up into new Hfe, and 

 forms flowers, fruits, and 

 seeds. In other cases, the 

 soft " herbaceous " stem 

 stiffens into woody branches, 

 the leaves become altered in 

 character, and assume the 

 form of petals or of stamens, 

 still further changes take 

 place in the pistils as they 

 ripen into the fruit, and 

 the ovules mature into 

 seeds. All these are phe- 

 nomena of development, 

 inseparable from growth, 

 but obviously different 

 from. it. 



The cultivator has con- 

 stantly to take account of 

 the two processes. To grow 

 a crop of Potatoes is one 

 thing, to secure a quantity 

 of "Apples," or Potato fruits 

 with their contained seeds, 

 is another matter. Again, 



the cultivator must bear in mind that, though 

 growth implies increased bulk, yet that increased 

 bulk does not necessarily imply enhanced growth. 

 The gigantic mangels and other roots that one sees 

 at shows are often of less value for feeding purposes 

 than others of smaller size. The reason is that the 

 bulk in the one case is principally made up of water 

 and of the extension of old rather than the multipli- 

 cation of new cells. The true test of value in such 

 cases is afforded by the microscope or by the chemist, 

 who finds a much larger proportionate amount of 

 "dry matter" (».«., matter left after driving off all 

 the water by means of heat) in the smaller than in 



the monster roots. Mere bulk, then, without growth 

 is of no practical advantage. 



The necessary conditions for growth have already 

 been mentioned in general terms under the head of 

 Germination. (See ante, Vol. I., p. 23.) With a 

 sufficient knowledge of general principles the culti- 

 vator can readily adjust his practice to particular 

 plants, and to his own particular requirements. It 

 may, however, not be in- 

 appropriate to allude to cer- 

 tain phenomena of growth 

 which it is especially neces- 

 sary to bear in mind. 



Continuous or In- 

 termittent Grrcwth 



Strictly speaking, growth, 

 at least in the higher plants, ' 

 is never absolutely con- 

 tinuouSjit is always arrested 

 at times to be resumed at 

 another period. But bear- 

 ing this qualification in mind 

 it is easy to see that, by 

 maintaining uniformity of 

 conditions, we induce more 

 or less continuous growth. 

 In forcing operations, where 

 the heat is regularly kept 

 above a certain temperature, 

 we have an illustration of 

 this. But even here it is 

 the practice to lower the 

 temperature at night and to 

 raise it in the day. At 

 night, though the tempera- 

 ture may not be deficient, 

 the light is absent, and it is 

 consequently good practice 

 to lessen the temperature so 

 as to secure a more even 

 balance of conditions. Even 

 in the tropics the night 



temperature, we must remember, is invariably lower 



than the day temperature. 



Day and Hight Growth. — Strange as it may 

 seem at first sight, there is no doubt that gTowth is 

 arrested in the day-time under the exposure to light 

 — not absolutely, but certainly relatively. The 

 energy of growth is decidedly greater at night than 

 in the day. During the day, when the leaves are 

 exposed to the action of the sun, food or food-mate- 

 rials are absorbed or transformed in the manner 

 already alluded to. The greater energy is devoted 

 during daylight hours to these processes. At night 



Pig. 61.— Experiment to show the Downward Ten- 

 dency of Growtli in Boots even when illuminated 

 from below. 



