NOTES ON ROOT-HAIRS AND ROOT GROWTH. 
177 
was placed in layers at different depths, then the root-fibrils 
were most abundant in those layers, and relatively few were 
present in the intervening less nutritions portions. The experi¬ 
ments were varied in different manners, but the results, in all 
cases, showed that the principal development of the roots 
occurred in the immediate vicinity of the material which was 
likely to furnish them with nutriment. 
On the general question of root-growth and root-absorption, 
however, the most -important recent paper is that of Sachs- 
in the “ Landw., Versuchstat.,” 1859, cap. iv., a summary of 
which is given in the French translation of Sachs’ ‘ 4 Physiologie 
Vegetale,” by Micheli. It is therein shown (p. 208, figs. 16—20) 
that the root fibrils insinuate themselves between the minutest 
particles of soil, that each particle of soil is invested like the fibril 
itself with a thin film of water which passes by diffusion into the 
root. In that work the observations of Liebig, Peters, Knop, and 
others are summarised. Sachs also alludes to some extremely 
fine thread-like protrusions from the root-hairs, which it would 
he interesting to compare with the protoplasmic outgrowths 
lately observed in leaves of the Teazel, by Dr. Francis Darwin. 
M. Moeller, whose researches are abstracted in the Bulletin 
of the Botanical Society of France (1878, t. xxv., Rev. Bibl.),* 
is stated to have sown seeds of Pinus Laricio in fifteen different 
soils. His general conclusions are that the length of the root is 
not in proportion to the total development of the plants. The 
length of the root depends upon the facility with which it 
penetrates the soil. In general, soils rich in humus produce 
thick roots ; pure mineral ones, slender ones. Lime produces 
little better roots than pure sand, while lime in combination is 
very serviceable to root development. Some varieties of soil 
favour the development of the cortex, others of the woody 
cylinder. Heathy soil produces the greatest quantity of wood. 
While in the root the diameter of the woody cylinder augments, 
in proportion with the growth of that organ, it is not so in the 
case of the stem, where it is the hark that predominates. It is 
in heathy soil that the woody portion of the plant is absolutely 
most developed. A limestone soil favours the wood at the 
expense of the bark. 
* Ueber den einflnss der Bodenbeschaffenheit anf die erste 
Entwickelung der Schwarzfobre (Pinus Laricio). 
