a Sphinx in some moist mould contained in a widemouthed glass bottle, covered with a lid. In watching the bottle from day to day, I observed that the moisture which during the heat of the day arose from the mould, became condensed on the internal surface of the glass, and returned whence it came; thus keeping the mould always in the same degree of humidity. About a week prior to the final change of the insect, a seedling fern and a grass made their appearance on the surface of the mould.

I could not but be struck with the circumstance of one of that very tribe of plants, which I had for years fruitlessly attempted to cultivate, coming up sponte suá in such a situation; and asked myself seriously what were the conditions necessary for its growth? To this the answer was,-1stly, an atmosphere free from soot; (this I well knew from previous experience): - 2ndly, light : 3rdly, heat:- 4thly, moisture:- and lastly, change of air. It was quite evident that the plants could obtain light and heat as well in the bottle as out of it; and that the lid which retained the moisture likewise excluded the soot. The only remaining condition to be fulfilled was the change of air; and how was this to be effected? When I published my account in the Companion to the Botanical Magazine,' I overlooked the law respecting the diffusion of gaseous bodies, described in the preceding chapter, and stated that this change was produced by the variations of temperature causing alternate expansions and contractions in the air surrounding the plants, and which of course produced a certain but very limited effect.

Thus, then, all the conditions necessary for the growth of my little plant were apparently fulfilled, and it remained only to put it to the test of experiment. I placed the

bottle outside the window of my study a room facing the north, and to my great delight the plants continued to grow well. They turned out to be Lastræa Filixmas and Poa annua. They required no attention, the same circulation of the water continuing; and here they remained for nearly four years, the Poa once flowering, and the fern producing three or four fronds annually. At the end of this time they accidentally perished, during my absence from home, in consequence of the rusting of the lid, and the admission of rain water. Long before this occurred, however, I procured for the purposes of experiment some plants of Hymenophyllum and Trichomanes ; and perhaps the most instructive way in which I can communicate the results of my enquiries will be to select a few out of numberless experiments, in the order in which they occurred. To commence with

1. Trichomanes speciosum; (the T. brevisetum of most English botanical works). This, the most lovely of our cellular plants, is the most intractable under ordinary methods of treatment. Loddiges, who have had it repeatedly, never could keep it alive; * and Baron Fischer, the superintendant of the botanical establishments of the Emperor of Russia, when he saw the plant growing in one of my cases, took off his hat, made a low bow to it, and said "You have been my master all the days of my life." Whence then arises the great difficulty of cultivating this plant? It is simply owing to the occasional dryness of the atmosphere. Place the plant in one of my

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* Mr. Mackay, of Dublin, I believe is almost the only person who has succeeded in growing this plant well; and to him I am indebted for my present specimens, and for numerous other kind contributions.

cases, and thus secure a constantly humid atmosphere around it, and it will grow as well in the most smoky parts of London as on the rocks at Killarney, or in the laurel forests of Teneriffe: :

"Miraturque novas frondes."

This plant lived for about four years in a wide-mouthed bottle, covered with oiled silk, during which time it required no water; but having outgrown its narrow limits it was removed to some rock-work in my largest fern-house, where it now remains, covered with a bell-glass, and occasionally watered.

2. Hymenophyllum, with one or two species of Jungermannia and Mosses. These were planted nine years since, in the bottle in which my first experimental plants sprang up and perished. The soil is a mixture of peat mould, loam and sand, with as much moisture as it would retain when water was poured through it. This same water has served for the nourishment of the plants up to the present time, nor am I at present able to assign any limit to their existence in this state. The mould appears to be as moist and the plants as fresh, as on the day they were enclosed; and when we reflect upon their independent state, we may, without any great stretch of imagination, carry our minds back to the primeval condition of vegetation, when "the Lord God had not caused it to rain upon the earth, and there was not a man to till the ground. But there went up a mist from the earth, and watered the whole face of the ground."

This will be a fitting place to make mention of a small but most interesting bottle which I received in October, 1837, from Mr. Newman, superintendant of the

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Botanic Garden at the Mauritius. The bottle was filled with two or three specimens of a little species of Gratiola and of Cotula, and tightly covered with painted canvas. The plants were in full flower. I placed them in a window with a southern aspect: they remained in vigour for six or seven weeks, when one after the other declined, and eventually all perished without ripening any seed, in consequence of the too great humidity of the atmosphere. Before this took place I observed, as in my first experiment, several seedling ferns making their appearance between the internal surface of the glass and the mould, and therefore allowed the bottle to remain in the same situation, which it has occupied to the present time, the cover never having been removed; and it is now a truly beautiful object. The upper part of the bottle is completely filled with the fronds of two species of Adiantum and one or two other species of ferns, and the lateral surface of the mould is densely coated with seedling ferns in all stages.

We may learn a few useful lessons from this little bottle. We see how abundant the seeds of ferns are, and how easy it would be to procure many species of these plants from distant countries, by collecting here and there a handful of the surface-mould, and, at any convenient season, placing this in a condition favourable for their development. To those cavillers who are continually questioning me as to the utility of ferns in creation, I answer, that one of the useful purposes which they serve, in common with numerous other cellular plants, is that of furnishing mould in situations where other plants of a higher order could not at first grow; and this is effected in a two-fold way by the decay of their fronds and the action of

their roots. Mr. Webster, in his account of the voyage of the Chanticleer, states that in the course of his ramble in the Island of St. Catherine's, when gathering ferns, he was particularly struck by observing that each plant had formed for itself a bed of fine mould, several inches in depth and extent, whilst beyond the circle of its own immediate growth was naked rock; and this appeared so general that he could not help attributing the extraordinary circumstance to the disintegrating power of their fibrous roots, which penetrated every crevice of the rock, and, by expanding in growth, appeared to split it into the smallest fragments.

Having determined the complete success of this mode upon more than a hundred species of ferns, and my ideas having a little expanded, I built a small house about eight feet square, outside one of my stair-case windows, facing the north; and, proceeding from ferns to those plants which live in their company, filled it with a mixed vegetation. This is called

3. The Tintern-Abbey House; from its containing in the centre a small model, built in pumice and Bath stone, of the west window of Tintern Abbey. The sides are built up with rock-work to the height of about five feet, and a perforated pipe runs round the top of the house, by means

* The Opuntia, or Prickly Pear, when placed in fresh fields of lava, which, in the ordinary course of nature,―i. e. by the successive growth and decay of lichens, mosses, and other cellular plants, would require a thousand years to become fertile, renders them capable of being converted into vineyards in the course of thirty or forty; and this by the comminuting action of its roots. Indeed, in all cases, the formation of mould may be traced to the double cause of the decay of dead vegetable matter and the splitting power of living roots.