1 RR i^Bausts the spirit of vegetation : "Aence a slighter degree of cold will destroy such fibres ; because, after having been excited for a consider- able time by a more powerful sti- mulus, they will cease to act on the application of one that is v/eaker, so that in consequence of hot days, tender plants are more liable to perish from the coldness of the night. For this reason, gardeners inthe more northern cUmates, shel- ter both the flowers of apricots and the tender vegetables, during the spring-frosts, from . the meridian sun, as well as from the destructive cold of the night, which is general- ly the most intense about one hour before sun-rise. In t e hot days of the month of J"une, 3793. Dr. Dak win twice observed several rows of garden- bea.ns to become quite sic' )y; and some of them even died, in conse- quence tvf being irrigated for one or two hours with water from an adjoining canal. This circumstance he attributes to the sudden appli- cation of cold, after t:.e plants had been greatly enfeebled, and de- prived pf their irritability by the excessive heat of the season, ra- ther than to the too copious water- ing of the dry soil. Some vege- tables, however, such as Straw- berries, onions, &c. which were equally exhausted, are less liable to be thus injured, and even re- ceive benefit from occasional irri- gation in dry and sultry weather. On the contrary, the spirit of vegetation acquires additional vi- gour, if plants have been exposed for a considerable time to a less than Usual degree of heat; but, if they be suddenly removed from a cold to a warm p. ace, they will experience a similar fate with those hapless persons^ to whose frozea i^k [35 limbs sudden heat v/as imprudent- ly applied : thus, too great in- crease of adion occasions inflam- mation, which is generally suc- ceeded by mortification and death. This fa^-l has been ascertained and confirmed by the experiments of M. VanUslar, who kept two species of the spurg' > nr wartwort, namely, the EupkornL Peplus, and Esuhi L. secluded ffom the light and heat, with a vievv- to render them niore irritable : on exposing these plants after v/ards to a meri- dian sun, they became grangren- ous, and in a short time decayed. .The increased, ordiminished, de- gree of iriitahihty in plants, is by Dr. Darwin attributed to their previous habits, with respeft to the stimulus of greater or less heat. Thus, the peno s at which vegeta- bles thrive in thesipring, appear to be greatly influenced by their ac- quired habits, as well as by their present SI nsiljfity to h.at: hence potatoes will germinate . in a much cooler temperature during the spring than in autumn ; hence also, the vernal months are the rcost fa- vourable to the process of making good mait ; because the barley will then sprout vi;ith a less degree of heat than at any other season. The irritability of plants has been discovered to be g cater in the morning than at noon, and less in the evening than at midday; though it is considerably augment- ed during cool and rai;iy weather. In a similar manner, the limbs of animals acquire a greater sensibi- lity of heat, after having been ex- po.-.td to the cold • thus, tl e hands, afier immersing them for a short time in snow, glow willi warmth on entc ring the house j — and the late cekbratid SPALLANZANiob- servcd several animals and in- .D 2 setts.
