134 BOTANY. 



the later growth of any member that it becomes distinct ; in 

 other words, every member is a modification of, and develop- 

 ment from, the general plant-body. Likewise, where equiva- 

 lent members have a different particular form or function, 

 it is only in the later stages of growth that the differences 

 appear. All equivalent members are alike in their earlier 

 stages, whether, for example, they eventually become broad 

 green surfaces (foliage leaves), bracts, scales, floral envelopes, 

 or the essential organs of the flower. 



167. These facts make it necessary to have some general 

 terms for the parts of the plant-body, which are applicable 

 to them in all their forms. We must have, for example, a 

 term so generalized as to include foliage leaves, bracts, scales, 

 floral envelopes, and all the other forms of the so-called leaf- 

 series. So, too, there is need of a term to include stems, 

 bulbs, bud, and flower axes, root-stocks, corms, tubers, and 

 the other forms of the so-called stem-series. 



168. By a careful study of the members of the more 

 perfect plants we find that they may be reduced to four 

 general forms, viz., (1) Caulome, which includes the stem 

 and the many other members which are found to be its 

 equivalent ; (2) Phyllome, including the leaf and its equiva- 

 lents ; (3) Trichome, which includes all outgrowths or ap- 

 pendages of the surface of the plant, as hairs, bristles, root- 

 hairs, etc. ; (4) the Root, which includes, besides ordinary 

 subterranean roots, those of epiphytes, parasites, etc. 



169. As indicated above, in the lower plants the differ- 

 entiation into members is not so marked as in the higher, 

 and in passing downward in the vegetable kingdom groups 

 are reached in which it is inappreciable, and finally in which 

 it is entirely wanting ; such an undifferentiated plant-body 

 is called a Thallome, and may properly be regarded as the 

 original form, or prototype. 



17O. Thallome.* The simplest thallome is the single 

 'cell ; this, though generally rounded, is, in some cases 

 (Botrydium, Caulerpa, etc.), irregularly extended into 

 branch-like or leaf-like portions, which must not be mistaken 



* From the Greek t?a//i)9, a young shoot, branch, or frond. 



