1819.] Direction of the Radicle and Germen. 263 
It is true that some botanists have regarded parasitical plants 
as being altogether destitute of roots, applying to them the term 
arrhiza, end, perhaps, Linneus may be squeezed into the num- 
ber; because in his distribution of the parts of the plant, he 
describes only a parasitical stem, and says nothing of a parasi- 
tical root; * though Linnens’s authority will not, perhaps, be 
segarded as of much weight in this case, when it is recollected 
that he elsewhere | represents the stems of all trees and shrubs 
as being merely roots above ground. But the most scientific 
definitions or descriptions of the root, amongst which I include 
those of Malpighi and Du Hamel, as well as that of our worthy 
and learned President, Sir J. E. Smith, { do evidently include 
parashien) plants ; because they represent that part of the plant 
y which it attaches itself to the substance on which it grows or 
feeds, as being the root. Besides, there are some parasitical 
plants that have even conspicuous roots, as any one who has 
ever seen a mature and complete plant of Orobanche major will 
acknowledge; and although systematic botanists do describe 
some plants of the class crypkoganua 2s being destitute of roots, 
because they have no visible or conspicuous root appearing as a 
distinct organ, yet the phytologist knows that this 1s not abso- 
lutely correct. 
We may regard the embryo of the misseltoe, therefore, as 
being furnished with a radicle, though not very conspicuous ; 
and it need not be thought strange if it grows occasionally 
upwards. We find that roots in general possess @ capacity of 
accommodating themselves to circumstances in the direction 
which they atiect, independent of, and even in opposition to, 
gravitation. ‘The roots of trees, which are planted in a bottom, 
near to sloping banks, will extend not merely in a horizontal 
direction, but will follow the direction of the ascent. An ash 
tree which is so situated, and is now within my view, has roots 
at the distance of five yards from the trunk elevated at least 
three feet above the level of the collar. Ifa piece of the root of 
the horse-radish, Cochlearia armoracia, is planted at the depth 
of 15 inches, it will send up root shoots erect to the surface of 
the soil;§ and if it is planted at the surface of the soil, it will 
no doubt send down root shoots to the same, or to a greater 
depth. There are even some stems, OF at least fronds, that seem 
to be wholly indifferent to the direction in which they grow. 
Many of the lichens which grow upwards when situated on the 
upper side of a branch, are very well content to grow down- 
wards when situated on the under side, ov to grow horizontally 
when attached to the surface of an upright trunk, The lichen 
prunastri may be quoted as an exam sle. Further, if gravitation 
were the sole cause giving direction to the root, there would be 
no such thing as a root’s selecting the best soil, which roots are 
* Phil, Bot. sect. 82. +-Lbid, sect. 80. 
4 Introd, to Bot, 102, § Mawe’s Gardener’s Dictionary. 
