24 CELLULAR TISSUE. 



globules. This phenomenon, then, in the present state of our 

 knowledge, must be placed among those facts, which can re- 

 ceive no other solution than that of referring them to a vital 

 force as their cause. That we need seek for no physical 

 cause, seems to me evident from the numerous researches and 

 experiments of Dutrochet. In all cases where suspension or 

 acceleration v/as produced by any agent, reaction took place 

 sooner or later where life was not destroyed, which would 

 not take place did its movement depend on a physieal power, 

 so far as we are acquainted with the operation of physical 

 forces. Reaction of such kind never takes place but under 

 the control of vital power. From the above facts it seems we 

 are warranted in the assertion that the seat of vitality in plants 

 resides in the globules attached to the internal walls of the cells. 



Those who are desirous of examining the subject in all its 

 bearing will find abundance in the original memoirs of Slack, 

 Pouchet, Mayen, Mirbel, Raspail, and Dutrochet; most of 

 them published in the Annalles des Sciences Naturelles, also 

 in Lindley's Introduction to Botany, Raspail's Physiologic 

 Vegetale, and in his Chimie Organique. 



23. The above description of a cell and its circulation, 

 applies to all the cells of the lower orders of plants at least ; 

 but in the higher orders, vv^e have a somewhat different ar- 

 rangement. 



In some cells comorisino; the tissue of leaves, the hairs of 

 plants, and the ovule before impregnation, a body has been 

 observed for some time past : but which has received but lit- 

 tle notice till quite recently. We are indebted to Schleiden 

 for a more minute examination into the constitution and func- 

 tions of these nuclei. He calls them Cytohlasts, which are 

 of a roundish or linticular form, and of a white or yellow 

 color. Tiie Cytoblast is usually of a granular structure, and 

 of various decrees of consistence — sometimes soft, and at 

 others of sufficient hardness to resist considerable pressure. 

 The origin of the cytoblast is sT,id to be from a minute body, 

 around which the other parts of the cytoblast are formed. 

 "If the gum which is found in the youngest albumen of a 

 plant be examined, it will be found turbid with molecules of 

 extreme minuteness. Of these, some acquire a larger size, 

 aud a more definite outline than others ; and by degrees, Cy- 

 tohlasts appear, which seem to be a granular coagulation round 

 each molecule. As soon as the cvtoblast has attained its full 

 size, there appears upon it a fine transparent vessicle. This 

 is a young cell which continues to swell out, and its lining 

 becomes formed of jelly, with the exception of the cytoblast, 



