THE FARMER'S MAGAZINE. 



resulting in continued or periodical change, is the sign of 

 the existence of this vital force— that force whose laws 

 form the subject of vegetable physiology. The collective 

 functions of a ])lant or animal constitute its life. I will 

 now confine myself to the consideration of the life of plants, 

 consisting in the performance of their collective functions 

 by the dilferent organs. Now, these functions collectively 

 constituting tiie life, exhibit what we call the constitution. 

 When we say that a plant has a particular constitution, we 

 mean tliat it performs its functions in a particular way. It 

 is to the examination of the constitution not only of plants, 

 but of the organs or parts of plants, to which vegetable 

 physiology has especially to direct its attention ; and I wish 

 to-day briefly to indicate some points of importance in 

 regard to this subject — the constitution of plants or their 

 organs. 



Iq the first place, I would direct attention to the pheuomeDB 

 illustratmg the existence of conatitutious iu species or kinds 

 of plants. The phenomena which prove these are familiar to 

 every one. Every one knows, for example, that Chickweed 

 fl)wer3 in the winter season, when the great proportion of the 

 plants growing in this country are unable not only to form 

 flower or seed, but even to put forth their leaves. The irrita- 

 bility (to use a somewhat hypothetical expression) or the vital 

 activity of this plant is evidently very different from that of 

 the majority of plants in this climate ; the particular irritability 

 there denotes its constitution ; it is the constitution of the 

 plant which causes it to pass through these changes under 

 different conditions from other plants, scarcely distinguishable 

 probably in the majority of their characters. There is notiiing 

 known, and probably nothing to be known, in the case of 

 Chickweed, to distiaguish it chemically from many other 

 common weeds, but it is the peculiarity of the constitution 

 of that species, that it passes through these changes under dif- 

 ferent conditions. Abundant illustrations of these peculiarities 

 might he readily furnished, with which it is scarcely worth 

 while to take up your time; for instance, the late flowering of 

 the Ivy in November, the flowering of the Hel'ebore or Christ- 

 mas Rose in January, and so on, as contrasted with the sum- 

 mer and autumn flowers, forming the great mass of our native 

 and cultivated vegetation. These peculiarities of constitution 

 are not entirely explicable by the view which has been taken 

 by some authors, that plants are dependent for their growth 

 upon a certain supply of heat given to theuo. Some years ago 

 M. Boussingault published some interesting researches, iu 

 which he showed that many plants, especially cultivated plants, 

 required a certain sum of heat for their perfect development ; 

 that between the time of the germination of the seed and 

 the ripening of the fruit, or the production of the grain, the 

 plant required to receive a certain amount of heat. He 

 measured this heat by taking the daily mean temperature and 

 multiplying it by the number of days, and he found that 

 the plants received pretty nearly the same amount of heat in 

 very different climates. Where the heat was greater the plant 

 was perfected in a smaller number of days ; where the heat 

 was less a greater number of days was required. For instance, 

 in Alsace, where his own property was situated, he found that 

 Barley would be perfected in ninety-two days, where there was 

 an average temperature of 19 deg. of the French thermometer, 

 giving a total of 1,748 deg. He then obtained the Date from 

 Cumbal, situated under the equator, where the plant was grown 

 between June and November, instead of between May and 

 August ; the daily temperature was there (it being in the colder 

 season) between 10 ar>d 11 degs., and 168 days were required 

 for the perfecting of the plant, giving a total result of 1797 

 degs, Iu many cases the uurahers came out very 5Bti8factorily for 



this hypothesis, showing that ttie plants required a certain 

 sum of heat, and that that heat might be given in small pro- 

 portions during a large number of d>»yR, or in higher propor- 

 tions iu a small number of days. However, there were many 

 important exceptions to this rule, thoae depending on certain 

 matters of detail which were ovetlookel in the first experiments. 

 For instance, Bousaingault did not pay attention to the omission 

 of useless heat. Many plaats do not move at certain tem- 

 peratures, even far above the freezing point. No plant, pro- 

 bably, will vegetate or perform any of its vital, functions undcj 

 the freezing point : many require several degrees above freez- 

 ing point before they begin to start into life. That must be 

 ascertained in each individual plant before we can calculate 

 the useful heat which it receives, as we must omit all degrees 

 below the point at which the plant moves. Then it is im- 

 portant to take into account the temperature of the soil, upon 

 which the development of plants very greatly depends. We 

 have no more striking illustration of that than was furnished 

 by the records of last year, when the temperature of the soil 

 in this country was found far sbove the average during the 

 later months, the result of which was the flowering and even 

 the ripening of seed in many plants, which very rarely perfect 

 their fruit in this country. Though the consideration of the 

 constitution of many plants may be reduced practically to a 

 consideration of the climate— the supply of heat varying with 

 the length of time during which the plants grow— still there 

 are limits to these conditions. Supposing the calculations 

 to be carried out with the precautions to which I have 

 just referred, there are certain limits beyond which they 

 cannot be admissible. Over-supplies of heat do not produce 

 the same results in ». shorter time, but produce disease; and 

 cold below a certain temperature will prevent the perform- 

 ance of the vital functions at all. ft is well known that in 

 the Feroe islands and in Iceland the amount of heat is never 

 sufficient to produce the ripening of the seed of grain, even 

 though the vegetation of the plant be prolonged to a much 

 greater extent than in this climate; there is not a sufficient 

 stimulus ever given to the plant, so that the natives are 

 obliged to import their seed, though they grow the grain year 

 after year. Again, we may note the information furnished by 

 travellers in regard to vegetation on the island of IMadeira, 

 There, in the season when the mean temperature approaches 

 that of our own summer, our Beech loses its leaves and remains 

 without them for 149 days ; the Oak remains without its leaves 

 110 days, the Vine 157 days. The Vine again affords an 

 example of the noxious results of excessive heat, because in 

 climates near the equator the plant scarcely produces fruit, or 

 only fruit of a very imperfect character, runnmg away to vege- 

 tation, and losing those qualities for which it is most valued. 

 This constitution of particular kinds of plants is a subject of 

 great importance both to the agriculturist and the horticul- 

 turist, and its practical influence has strongly attracted stten- 

 tion in those valuable experiments which have been carried on 

 at Rothamsted by Messrs. Lawes and Gilbert. There they 

 have found most important differences, not only between such 

 plants as Turnips and Grain crops, but also differences of con- 

 stitution between Barley and Wheat— plants belonging to the 

 same natural families, and differing (scientifically speaking) 

 only in slight peculiarities from each other. 



We cannot doubt the existence of this peculiar constitution 

 in species of plants. But going a step beyond this, we find 

 that individual plants have their constitutions, and the result 

 of this variation within the limits of particular species is to 

 produce plants having characters considerably different from 

 each ether, and yet referable all to the same speciCc type. 

 Species of plants are subject to vaiiatiom according to externa 



