412 Prof. H. Karsten on the Formation, 
We here find, therefore, in the development of these two phy 
siologically different organs, a similar phenomenon to that which 
obtains in compound plants; for all those parts of vascular 
plants which belong to the ascending axis are clothed during 
their development by the epidermis; whereas this covering is 
wanting to the root, whose divisions are invested with a layer of 
tissue analogous in many respects to cork, even at their growing 
extremities. 
The normal phenomenon of root-formation from the original 
lower extremity of the cell of the Conferva, isolated in the manner 
described, and that of the production of a branch from its original 
upper end (exceptions to which rule are extremely rare) render 
it evident that in each of these cells there is a physiological dif- 
ference between the two extremities. Moreover, in the case of 
the swarm-spores and gonidia of Algze, which consist of only one 
system of endogenous cells, and are provided on one side with 
vibratile cilia, a similar pre-existent polarity may be recognized; 
for, in these, one side, and indeed that which is clothed with 
cilia, will always grow downwards into the root of attachment, 
whilst the opposite extremity of the spore, invested by the 
thickened mother cell, grows upwards to form the stem. This 
separation of the regions of the cell by reason of their endow- 
ment with different functions, which is already established by 
development in the parent plant, forms the basis of the dissimi- 
larity in the arrangement of the organs of the developed plant. - 
In part it is the mode of nourishment of the spores and ger- 
minal cells, dependent on their position in the mother cell and 
in the parent plant, which engrafts upon the cell, simultaneously 
with its production and development, the dissimilarity in the 
functions of its different regions. 
In part, also, this heterologous activity at the opposite poles 
of many germinating spores of Alge and of the phanerogamic 
embryo in course of development, is probably founded in the 
anatomical difference of these poles—the extremity of the young 
organism which takes on the function of a root breaking through 
the mother cell which continues to envelope the opposite ex- 
tremity as an enclosing membrane, or at least envelopes its 
youngest parts until the complete evolution of the normal form. 
We may further look upon the vibratile cilia with which the 
germinal corpuscles are furnished as in part a cause of their 
polarity; for the cilia themselves, being extended hair-like 
secretion-cells (Bot. Zeitung, 1852), constitute the first simple 
organs of nutrition of the embryonic organism. Filled with a 
liquid which causes the taking-up of matters from the surround- 
ing medium, these organs doubtless prepare the first nutritive 
matter for the cell upon which they are seated ; and this matter 
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