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 Algse, 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 Algse 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 



