A plant which has no means of migration when it has exhausted the nearby food supply is manifestly at a disadvantage when compared with a progressive rhizome plant which moves every year into a new and fresh location. To be sure, the distance it travels may not be far but it is enough to remove the plant from an exhausted position and from its wornout and useless tissue. Thus this group of plants may be said to have found the secret of potential immortality, for, unless some catastrophe overtakes them, they may live indefinitely and remain young. It is interesting in this connection, to note how far some of these plants travel in a century. This may be calculated in a general way by measuring the annual growth in length of the rhizome. Solomon’s Seal travels from twelve to twenty feet in this length of time, Uvularia perfoliata L. from eight to ten feet, Onoclea sensibilis L. from three hundred to five hundred feet, and others still farther.
The Iris group are exceptions, in that they travel in a circle. The reason seems to be that the lateral branches which continue the rhizome from year to year mostly arise on the same side of the terminal bud, so that each branch goes off at a slight angle to the former branch. The degree of angle determines the size of the resulting circle. One class of rhizome plants is very distinct and requires especial mention. This class may be termed upright or retrogressive rhizome plants. The upright rhizome may originate from a progressive rhizome, or from a crown former or in some other way. Trillium nivale Riddell is in a transitional stage between the progressive and retrogressive classes, since the large rhizomes are upright and the young lateral branches are progressive until they have traveled some distance away from the parent rhizome, when they too, become upright. The lower Ferns (Ophioglossaceæ) belong to this class. The disadvantage of this habit is that the rhizome will soon grow out of the ground and be in a very exposed condition. To counteract this tendency the roots of these plants are usually strongly contractile and pull the rhizome down into the ground as fast as it grows out. Skunk Cabbage (Spathyema foetida (L.) Raf.) has an upright rhizome and root contraction is very marked. The very apparent disadvantages of the retrogressive or upright rhizome habit have made this class very few in number compared with the progressive rhizome class. In Ohio there are about 475 species of rhizome plants and less than twenty-five of these belong to the retrogressive class. This class is closely related to the corm plants, indeed, all that is needed to make the typical corm out of a retrogressive rhizome plant, such as Trillium nivale, is to shorten and make more definite the annual growth of the rhizome. The bulb is usually a very short, upright rhizome with many thickened scales. The bulb of Lilium martagon is of this kind but that of Lilium canadense is more closely related to the progressive rhizomes. The parent bulb sends out one or more thick rhizomes which grow outward if the bulb is at the normal depth, downward if the bulb is too near the surface of the ground and the new bulbs are formed by the shortening of the outer end and the growth and thickening of the scales of the rhizome.
Both bulbs and corms may be regarded as rhizomes modified to suit peculiar conditions, such as a long, dry, heated period alternating with a short, rainy period. A plant to survive under such conditions must be able to start up very quickly as soon as the rains come, and flower and mature its seeds before the drouth again overtakes it. A large amount of food material must be stored up by the plant in order to do this, and the food material must be kept from drying or burning up during the heated period. Bulbs and corms, protected as they usually are by dry and coriaceous coverings, answer these requirements and are usually abundant in localities where these conditions obtain. Bulb and corm plants are also well fitted to live in dense woods where the light is soon shut off in the Spring by the expanding leaves of the trees. They are able to spring up very early, flower and ripen seeds before the light is shut off. The food supply which enables them to do this is often protected by acrid or poisonous principals developed in the bulb or corm. Pepper-root (Dentaria laciniata Muhl.) and Jack-in-the-Pulpit (Arisaema triphyllum [L.] Torr.) are examples.
Crown plants, while not true geophytes, are often closely related to rhizome plants and may be regarded as transitional. They are formed by the freezing back of the upright stem to the surface of the ground, and the survival of the short stem beneath the surface until the next Spring when it sends out branches from adventitious buds. In this way several branches are sent up where there was one before, and, as this crowds and injures the plant, these branches usually move out some distance from the base of the parent plant before coming to the surface. The connection with the main stem is often severed, and thus many new plants are formed. All this rarely takes place in the Spring but has been shifted back to late Summer or Fall by the parent plant. Often a food supply is stored up for the young plants by the parent. Helianthus tuberosus L. is a good example.
Vegetative propagation is brought to its highest development in this class and they become our worst weeds.
NOTES ECONOMIC AND TAXONOMIC ON THE SAW BRIER, SMILAX GLAUCA.
W. A. Kellerman.
(Plate [4].)
In a recent trip through some of the southern counties of the State my attention was arrested by the enormous quantity of Smilax glauca—Glaucous-leaf Brier as given by Britton in the Illustrated Flora—but generally and appropriately called in these regions where so abundant, the Saw Brier. In the sandy soil of Hocking County, thence southward to the Ohio River this plant may be seen growing in field and pasture, by roadside and on hillside, and everywhere except in wet soils and dense woods. It climbs over fences and high bushes, displaying its bright foliage of lively green, more effective by contrast with the abundant white bloom on the under side. In the Autumn it presents showy wreaths of black but glaucous-coated berries and the most gorgeous coloration of foliage. The leaves remain for the most part late in Fall and Winter, and for brilliant and delicate shades of rose and red are not surpassed by any plant of our entire flora. The forbidding aspect of the long, wiry stems, with their bristly covering of long, saw-like or needle-shaped prickles, serves also to distinguish this plant even among the attractive associates of its kingdom.
A Bad Weed.—As a weed this species here stands at the head of the list. Its horrid prickles make it one of the most disagreeable plants with which to come in contact. It revels in the pastures and clambers over the fences; it flourishes in the meadows and fields, and no ordinary practice of crop-cultivation interferes with its luxuriance. One can readily see that it is not carelessness on the part of the farmer that suffers half or still larger portions of his fields to be covered with this pestiferous vine. No other weed is seen in the area and therefore he has been diligent and careful in his tillage. The meadows even if twice or thrice mowed in a season will yet contain year to year the same quantity of Saw Brier. The stems spring up quickly, and grow “a foot in a night” the people say; surely the Saw Brier is the freshest plant in the field. In a case specially noticed a garden spot had been put in cultivation in 1873, and has been continually and thoroughly cultivated every year since, yet the Saw Brier is there to-day.