110 ANATOMY AND PHYSIOLOGY OF 



properties of a special variety, yet tHs is an exception to the rale Every 

 part detaclied from a plant retains this agreement after its separation^ and 

 thus propagation by division affords tlie means of mnlliplying certain 

 varieties wHck could not, or only witli imcertainty, be propagated by 

 seed. Cases certainly do occur in gTafted trees where the composition of 

 the sap of the stock exercises a certain influence upon the characters of the 

 fmit of the graft, but on the whole, this is an exception. (Gartner has 

 given a comparative account of the observations on this subject, in lus 

 ^^ JSxperi^nents andOhserv. on Hybridation'' — " Versuchen und Beohacht uh 

 du Bastardhldiingp 606 ) 



h Fropagation hj Spores and Seeds, 



In all vegetables which attain their full normal development, 

 the period of vegetation is succeeded by that of fiuctification, 

 ■whether, as in the lower plants, the same cells which in youth 

 executed the vegetative functions, in their subsequent period of 

 life become organs of fructification, or, special organs of fructifica- 

 tion become developed. 



Observ. The universality of this pro]3osition is truly only borne out by 

 analogy with the majority of plants, for in the present condition of our 

 knowledge we cannot determine whether all vegetables fructify. In many 

 lower plants we are still unacquainted with any fructification, either be- 

 cause they are really defi.cient in them, as may be possible for instance in 

 the Yeast-plant, or that we do not know all the stages of their develop- 

 ment. The latter is the case in many lower plants ; the difficulty of study- 

 ing them is increased by the fact that a large number of forms have been 

 described as peculiar species, especially among the Algse, wliicli are only 

 earlier stages of development, and in many cases abnormal examples pro- 

 duced by imfavourable external conditions of plants frequently belonging 

 to totally different families. 



The organ destined for a germ may always Ibe traced back to 

 an origin from a single cell. When this cell, at the epoch of its 

 sepai^ation from the parent plant, contains no rudiment of a new 

 plant, but only an organizable fluid, or, in rarer cases, a few 

 secondary cells firmly blended with its membrane, and this cell, 

 after its separation from the parent plant, under the influence of 

 external circumstances favoxn-aHe to the excitement of vegetation, 

 grows up directly into a new plant through expansion of its mem- 

 brane and production of new cells in its interior, this is called a 

 spore (spora, keimkoroi). The formation of spores takes place 

 without fertilization, and plants wliich are propagated by spores 

 are termed Gryptogawiia or Exemhryonaias. 



When, on the other hand, the propagative cell (as emhryosac) 

 forms part of a compound organ, and through previous impreg- 

 nation, produces in its interior the rudiments of a perfect plant, 

 furnished with stem and root (the embryo, keim), and this becomes 

 detached with the enveloping parts formed by the further deve- 



