21 



CASSELL'S POPULAR GAEDEXING. 



out or from within, is checked by too low or too 

 high a temperature, the most favourable temperature 

 varying- with different plants and under different 

 circumstances. The absorption of water, however, 

 may be more fitly dealt with hereafter, under the 

 head of " Eoot-action." 



Digestion of Reserve Food. — The conversion 

 of the insoluble and indigestible reserve matters into 

 the soluble and digestible food-material is a very 

 marvellous and a very intricate process, one only 

 imperfectly known, and one to which we can only 

 incidentally allude. It must suffice to say that it is 

 effected by the action of a substance called ' ' diastase," 



practice to prevent the germinating seed from get- 

 ting too dry, or too cold, or too deeply buried in 

 the soil. On the other hand, they furnish sug- 

 gestions as to the best method of preserving seeds, 

 and of transporting them from distant countries. 

 These are points which will be further dealt with 

 under the head of "Seed-sowing." 



Not so well kao-^-n to practitioners are the means 

 whereby germination may, in some cases, be hastened 

 and facilitated. In the laboratory it is found that 

 solutions of chlorine, iodine, and bromine favoui* 

 germination, and this is accounted for by the fact 

 that water (consisting of hydrogen and oxygen gases 

 combined) is decomposed ; as for instance by chlorine 



Fi^. 10. — Tubers of Potato, serving as food-store. 



T/hich exerts its action only when the juices of the 

 plant are acid. Lately it has been shown that 

 certain extremely minute organisms or germs, com- 

 monly known under the general term of " Bacteria," 

 act on starchy matters in the same way as diastase ; 

 indeed, it is stated that they secrete a ferment 

 identical wdth, or having the same properties as, 

 diastase. The fatt3" and oily matters contained in 

 some seeds undergo corresponding changes, and arc 

 converted by the agency of a nitrogenous ferment 

 from an insoluble to a soluble condition. 



Conditions requisite for Germination. — 



Sufficiency of moisture and of heat, together with 

 access of air, then, constitute the chief essentials in the 

 germination of the seed or the sprouting of the bud. 

 These facts, coupled with an examination of the na- 

 ture of the seed, large or small, thick-husked or thin- 

 husked, with or without perisperm, and a knowledge 

 of the climatic conditions of the country from which 

 it comes, furnish the reasons for the care taken in 



under the influence of light forming hydrochloric 

 acid and setting oxygen at liberty, which "nascent" 

 oxygen, as it is termed, is forthwith appropriated by 

 the growing seed as a powerful stimulant and as 

 food. On the other hand, the application of anaesthe- 

 tics, such as ether or chloroform, arrests germination 

 for a time, the process being resumed after the effects 

 of the vapour have passed off. pro^-ided the dose be 

 not so strong as to destroy vitality altogether. 



Vitality of Seeds. — The length of time diu^ing 

 which seeds can retain their vitality is very variable, 

 being dependent on the conditions under which the 

 seed is kept, and on the nature of the seed itself, 

 as may readily be inferred from what has been 

 already said. Generally speaking it may be said 

 that oily seeds lose their ^-itality sooner than starchy 

 ones, owing to the greater readiness of the oil to 

 decompose. Even imder ordinary circumstances 

 there is great variation as to the duration of the time 

 for which seeds of different plants will preserve their 



