368 



CASSELL'S POPULAE OARDEXIXG. 



change, so long as sufficient nutriment were afforded 

 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, hut not developing into any other 

 stage of growth. So among higher plants we 

 have illustrations of the same thing in the fact that 

 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, supi^ly a little 

 more heat, a little less water 

 at particular seasons, a fuller 

 exposure to light, and the 

 lieretofore sluggish plant 

 wakes up into new life, 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 fvu-ther 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, thougli 

 growth implies increased bulk, yet that increased 

 bulk does not necessarily imply enlianced 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" (i.e., matter left after dnA-ing off all 

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



Fig-. 51. — Experimeut to sliow tlie Downward Ten- 

 deucy ol: Growth in Eoots even when innmiuated 

 from below. 



the monster roots. I\Iere 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 

 Gernrination. (See ante, Vol. I., p. 23.) AYith a 

 sufficient knowledge of general principles the culti- 

 vator can readily adjust his practice to pai-ticular 

 plants, and to his own particular requirements. It 

 may. however, not be in- 

 ==p==ap^_ appropriate to allude to cer- 



tain phenomena of growth 

 which it is especially neces- 

 sary to bear in mind. 



Continuous or In- 

 termittent Growth. — 

 Strictly speaking, growth, 

 at least in the higher plants, 

 is never absolutely con- 

 tinuous, it is always aiTested 

 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 gro\vi;h. 

 In forcing operations, w here 

 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 teniperatm-e 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 Night Growth.— Strange as it may 

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

 arrested in the day-time imder the exposm-e to light 

 — not absolutely, but certainly relatively. The 

 energy of growth is decidedly greater at night than 

 in the day. Dming 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 

 dui'ing daylight hours to these processes. At night 



