PHY 



OR, BOTANICAL DICTIONARY. 



PHY 



301 



diately after their evolution. We would require still further 

 observations on this point, especially in the small Fungi, and 

 even in these, different modifications may possibly appear; 

 but this is merely a supposition about which nothing certain 

 is known. Most of the plants which have this peculiarity 

 are so very small, that their existence and characteristic 

 varieties can be perceived with difficulty, much less is an 

 accurate knowledge of such very minute plants to be expected. 

 Nemoblasta. These appear in Mosses and Filices, and may 

 perhaps be found also in Algae. To prove their existence 

 in the last, however, we still need more accurate observa- 

 tions. The substance of the cotyledon in them divides into 

 two halves, and bursts into an irregular shape, resembling 

 threads. Plexeoblastae, are those in which the cotyledons ap- 

 pear above ground in two parts, and change into leaves, which 

 are of a different shape from the rest of the leaves. They are 

 elliptic in the species of Phaseolus; linear in the Umbellatae 

 and in the Plantago; cordate in the plants of the 16th class of 

 Liuneus; inversely cordate in those of the 15th class; reni- 

 fonn in the.riugent plants; wedge-shaped, and at the point 

 variously intersected, in the Lime-tree. Geoblastte, are those 

 which keep the substance of the cotyledons under ground, 

 c. g. the Vetch, Pea, the Gramina, Lilies, &c. They are of a 

 double kind: Rhizoblastce, where the seed has & rostel, and 

 shoots down a straight root, as in most plants belonging to 

 this class : Arliizoblasta;, when the seed wants the rostel, 

 as in some aquatic and parasitic plants. Spheeroblastce, are 

 those whose cotyledons are not disunited, but which come 

 out of the ground in form of little globules fixed u-pon a small 

 stalk, and have the plumula on" their side. This we meet 

 with in Juncus Bufonius, snbverticillatus, and some plants 

 related to it. Several botanists, who were unacquanted with 

 this singular mode of germination, have mistaken the above- 

 mentioned plant for a new one belonging to the 24th class 

 of Lianeus. 



" It has long been known, that every plant affects its own 

 peculiar soil, and that on this account seeds do not germi- 

 nate in all kinds of soil, at least they soon decay in a disad- 

 vantageous one. Various trials have been made, to make 

 seeds germinate in various matters, different from the usual 

 earths. Sukkow made salad plants grow in pounded fluat 

 of lime and barytes. Bonnet made plants grow in sawdust, 

 slips of paper, cotton, and even in an old book. That Cress 

 (Lcpidium sativum) germinates upon a piece of woollen 

 cloth, is a well known fact. Mr. Humboldt's experiments 

 to make seeds germinate in metallic oxyds, especially the 

 red oxyd of lead, and massicot, &c. are more instructive. 

 In powder of coal and sulphur, seeds germinated likewise 

 very well. He found that oxygen proved an extreme stimu- 

 lus to plants, and that without it they never can be brought 

 to germinate. On this account germination went on quickly 

 in metallic oxyds, especially in minium. In oil, on the con- 

 trary, carbon, hydrogen, in the filings of lead, iron, and 

 copper, as well as in the powdered molybdenc and in alkalies, 

 no one seed germinated. It soon occurred to him, that 

 with oxygen as a stimulant he might forcibly make seeds 

 germinate faster ; and he actually found, that at the tempe- 

 rature of 20 Reaum. all seeds vegetated most rapidly when 

 steeped in oxy-muriatic acid. One instance alone will suf- 

 fice. The seeds of the Lepidium sativum germinated after 

 six or seven hours, when put into oxy-muriatic acid; whereas, 

 when lying in common water, they required from 36 to 38 

 hours. In a letter dated February, 1801, he writes to me, 

 that in .Vienna they derived much benefit from the discovery 

 of this fact; and that seeds twenty and thirty yeSrs old, 

 brought from the Bahama islands, Madagascar, &c. which 



constantly refused to germinate, very readily, in this way, 

 vegetated, and produced plants which grew up very success- 

 fully. The Mimosa scandens, which as yet is not to be 

 found in any botanic garden, grew very well with this acid. 

 As every gardener cannot obtain the oxy-muriatic acid, Mr. 

 Humboldt proposes a very easy method to procure it without 

 difficulty. He took a cubic inch of water, a tea-spoonful 

 of common muriatic acid, two tea-spoonfuls of oxyd of man- 

 ganese, mixed it, and placed the seeds in them. The whole 

 was now allowed to digest with a heat of 18 to 30 Reaum. 

 In this the seeds germinate excellently; but it is necessary 

 to take the seeds out, as soon as the corcle appears. That 

 the seeds are not injured by the acid, is proved by the 

 many plants which have been treated in this way, under the 

 inspection of Mr. Jacquin, and in which vegetation went on 

 extremely well. It is the oxygen of the atmosphere which 

 stimulates the seed to germination. And this explains at once 

 the experiment of Mr. Achard, why plants vegetate faster 

 in very compressed air, than in air in its common state. Be- 

 sides oxygen, ammonia too favours the germination of seeds; 

 hence they germinate almost immediately when placed in dung, 

 which therefore serves as manure. Cow-dung, we know, 

 consists of muriatic acid and ammonia. In fluids which con- 

 tain no oxygen, seeds will not germinate. Thus they never 

 germinate in oil, which consists of hydrogen and carbon. 



" It is the rostel of seeds whichproduces the part of a plant 

 under ground, and which is called the descending stem or 

 root. But physioloists call that part only a root, which 

 carries nourishment from the soil to the plant, or what we 

 before called radicles or fibres. In under shrubs, this stem 

 descending under ground, consists of a bulbous, tuberous, 

 fibrous, or oblong root. In annual plants it is more or less 

 perpendicular; and in shrubs and trees its formation entirely 

 resembles the stem. In this, foresters again distinguish 

 two separate parts : the thick one, which descends perpen- 

 dicularly, called the main root; and those parts which run 

 forth horizontally in the earth, which are their horizontal 

 roots. Anatomy shews us, that in herbaceous and biennial 

 plants the adducent and pneumatic vessels form a circle in 

 the root, the inside of which is closely compressed, the out- 

 side lined with cellular texture. The reducent vessels lie 

 in this last; the lymphatics without apertures in the epidermis. 

 Roots are quite destitute of pith ; we never meet with more 

 than one vascular circle, for as the duration of the first is 

 only that of a year, or a few months, the new circle cannot 

 attach itself to the old. One exception to this we have in 

 the Beet, (Beta vulgaris,) which is a biennial plant: its root, 

 when about a year old, has from five to eight 'of these vas- 

 cular circles, as it is abundantly evident to any one who has 

 observed the Beet. It follows, therefore, that Beets produce 

 them more thr.n once, and they make an exception to the 

 common rule, which is worthy the notice of physiologists. 

 Under-shrubs, which have no bulbs, knobs, or creeping roots, 

 are provided with a concentrated circle of adducent and air 

 vessels, which is surrounded with a strong cellular texture 

 inclosed in the external integuments. Like all other roots, 

 they are quite destitute of the tube of pith. A new circle is 

 formed every year in such a manner that, at the part which 

 lies nearest to the surface, we can determine precisely the 

 age of the circle by the number of the. rings. The smallest 

 roots last many years, and are, according to the difference 

 of the species, revived by new roots, which supply the place 

 of the old ones when decayed. This is different in the 

 creeping, tuberous, and firm bulbous roots: they have, ac- 

 cording to their species, their vessels in a circle closer to the 

 centre, or more or less distant from it. They are, however, 



