THE SPECIFIC CONSTITUTION OF PROTOPLASM. 487 



detinition that Linnaeus considered these ancestors to be creations of the " infinitum 

 ens"; but it is very important that he recognized existing organisms as the 

 continuation, the rejuvenated portions of one and the same living being, so that 

 the species is not a figment of the human mind, but is something which actually 

 has an objective existence. 



Moreover, to decide which individuals are similar, i.e. of the same species, we 

 take note of characters apparent to our senses, especially of the form and structure 

 of the plant-body. Each species has its special features or characteristics, and all 

 individuals possessing these specific marks are said to belong to the same species. 

 Specific characteristics are hereditary, and are transmitted unaltered to the 

 descendants. There are, however, some plant characteristics which are not 

 inherited, but which may appear or not according as the individual develops in 

 this or that place, and these must be regarded as the expression of certain external 

 conditions which have an influence on plant-organization. They form the founda- 

 tion for the existence of the variety, according to Linnaeus. The individuals of 

 each species may vary, but the variations are not handed down to posterity; they 

 change according to position and other external influences. Systematic Botanists 

 since the time of Linn^us have therefore to consider two kinds of distinguishing 

 marks or characteristics: (1) those which are inconstant and not inherited; and 

 (2) those which are constant under widely different external conditions and are 

 hereditary. The latter determine the species, the former the variety. Each species 

 may exhibit several varieties at one time, but its specific characteristics remain 

 unaltered. If the specific marks should have undergone any alteration in the 

 descendants, these will form a new species, or rather the appearance of an in- 

 dividual furnished with new specific marks forms the starting-point for a new 

 species. 



The relations of outward form and structure relied on by systematic Botanists 

 in the identification of plant species depend of course on the plan of construction of 

 the protoplasm of the species in question, and again only the specific constitution of 

 the protoplasm determines this constructive plan. Before we can arrive at a 

 correct idea of the nature of species, therefore, it is above all things necessary to 

 obtain as clear a picture as possible of the relations of the protoplasm to the 

 external visible form. 



THE SPECIFIC CONSTITUTION OF PROTOPLASM. 



Mention has previously been made of the remarkable fact that the species of 

 a genus diflTering from one another in outward appearance also differ in respect 

 of the scents secreted by them. Many Roses have diflTerent scents (Rosa aljjina, 

 arvensis, cinnamomea, Gallica, Indica, Nasterana, pomifera, rubiginosa, sepium, 

 &c.), and a blind man could distinguish each species by the scent of its flowers. 

 This is also true of species the foliage, stem, and roots of which emit odorous 

 substances. By rubbing the foliage of different species of Thyme in one's fingers 



