THE LIFE -HISTORY OF PLANTS. 



23 



seeds from the points of view we have named will at 

 once supply the grower with a hint as to the method 

 of treatment most appropriate to them. 



Buds have no perisperm to draw upon for their 

 supplies, but they have nutritive matter stored up 

 within their tissues, and they have a still more 

 abundant supply in the bark and young wood of the 

 shoot from which they originate. 



The thick root of the carrot or turnip contains a 

 supply available for the growing bud, which forms the 

 crown ; the thick fleshy root-stock of such plants as 

 the Solomon's Seal {Convallaria), the tuberous roots 

 of dahlia or orchis (Figs. 8, 9), the tubers of the 

 potato (Fig. 10), the fleshy 

 stems of cactuses (Fig. 11), 

 the fleshy scales of the bulb, 

 also contain much nutritive 

 matter available for the 

 support of their growing 

 point. In the corm of the 

 crocus, the old corm serves 

 as a storehouse for the new 

 growths. 



We have now to see in 

 what way that store is 

 rendered available, and 

 what circumstances in- 

 fluence it — matters of the 

 gi-eater moment, seeing 

 that the food as it exists 

 in the perisperm or tissues 

 of the bud or seedling is 

 insoluble, and quite in- 

 capable of serving as food 

 untn it has been in some, 

 way rendered soluble, and 

 capable of being digested 

 and assimilated. 



Pig. 9. — Tuberous Boot of Orchis, serving as 

 food-store. 



Germination. — It 



hence appears that the bursting of the seed to liberate 

 the enclosed seedling, the unfolding of the scales to 

 let loose the young shoot, are phenomena dependent 

 on a gradual change in the nature of their contents — 

 a change brought about, in the flrst instance, by the 

 absorption of water, or at least by the transfer of 

 water from one part to another, under the influence 

 of the increasing heat of the soil or of the atmo- 

 sphere. It cannot be the result of the more intense 

 light of the lengthening day, for the seeds grow 

 beneath the soil away from the access of light, and 

 the buds or eyes will sprout in the darkest cellar, as 

 every one who stores potatoes knows to his cost. On 

 the other hand, every gardener knows what a little 

 " bottom-heat " will do to start his seeds or buds into 

 growth. 



Increasing heat, then, is the prime mover in start- 

 ing seeds and buds into growth, if the water sup- 

 ply from within or from without be adequate. The 

 amount of heat required is difierent in different cases. 

 Hardly has the soil of the Alps or of the Arctic re- 

 gions become loosened from the grip of frost than 

 growth commences. In other cases, nothing cooler 

 than the temperature of a hot bath sufBces to stimu- 

 late 'either bud or seed. Each plant grows best at 

 a certain temperatui'e ; high in one case, low in 

 another. What that temperature is, the physiologist 

 fixes precisely in the laboratory, and the practical 

 cultivator approximately by means of his experi- 

 ments, aided by what he 

 may know beforehand of 

 the source whence the seed 

 was derived, and its pro- 

 bable requirements. Under , 

 natural circumstances, in 

 temperate countries, the 

 he^.t of the soil, treasured 

 up from last summer's sun- 

 rays, is always greater 

 during the winter than 

 that of the atmosphere, so 

 that in many instances a 

 very little additional heat 

 in spring sufiices to incite 

 the dormant activity of the 

 plant. 



We are now brought face 

 to face with the question, 

 What does the heat do':' 

 In reply, it may briefly be 

 said that it disturbs the 

 balance both of the solids 

 and of the fluids of the 

 plant; it expands the 

 gases ; it causes currents 

 in them and in the fluids ; 

 it provokes chemical action ; it necessitates the ab- 

 sorption of water. What is the result of all this, 

 we shall have to consider further on. 



The absorption of water is the most important of 

 these early stages (provided the bud or seed have 

 access to oxygen gas, as it would always have under 

 ordinary circumstances). This absorption of water 

 is rendered evident by the increased size of the seed 

 or bud, an increase beyond what could occur at so 

 early a date from any growth, were that possible. 

 The water may be derived from without, or it may 

 in the fljst instance be simply transferred from one 

 portion of the bud, bulb, tuber, or seed, which has 

 much, into another portion which has little, no 

 living portion ever being absolutely destitute of 

 water. This movement of water, either from with- 



