154 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



origin and development of the individual are equally true for the 

 race. 



When we look for some common and immediate source of 

 the processes of development, whether in an individual or the 

 race, we find it to reside in living protoplasm. This complex 

 substance, together with its still more complicated nucleuses the 

 seat of all change in living structures. No one knows how it 

 is done, but we readily see the effect ; so that just as the 

 different parts or organs of a bird or reptile are formed out of 

 one and the same protoplasmic substances in the egg, so is it 

 in plants. Their organs are developed out of a common or 

 embryonic tissue. Out of this, by means of the protoplasm or 

 " physical basis of life," as Huxley called it, all the organs of a 

 plant can arise. 



This formative tissue, as a rule, always develops the same 

 organs in the right places ; nevertheless, it seems rarely to quite 

 lose the power of forming others, if it be necessary, in the place 

 of the usual organs. 



It is convenient to classify plant-organs as axes and append- 

 ages ; the former being roots, stems, and branches, while the 

 latter are the various structures which grow out of them, and 

 are the so-called "foliar organs"; such being the leaves, 

 stipules, leaf-scales, bracts, and the members of the four floral 

 whorls. 



Organs are said to be homologous when they are of the same 

 fundamental nature (i.e., axis or appendage, as the case maybe), 

 though their functions may be very different. Thus a potato is 

 homologous with a birch- twig, both being branches from the 

 stem. But organs having the same functions need not be of the 

 same nature. Thus the tendril of a pea is an altered leaf 

 (appendage), while that of a vine is a metamorphosed flowering 

 branch (axis). They are therefore analogous, in that their uses 

 are identical ; but they are not homologous as to their origins. 

 Each organ of a plant sustains what may be called its normal 

 use ; but by transformation it may assume other uses, and so 

 similatc analogous organs. 



I propose giving a few illustrations only of each organ to 

 exemplify these facts. 



Roots.— Roots and stems aro inoro or less anatomically 



