INAUGURAL ADDRESS. 239 



Lowest of all plants we place the Alga3, or the weeds of the sea 

 and fresh water — an immense class, embracing species most minute, 

 and some enormous in size. The minute species are the Diatoms, 

 which we place at the bottom of the scale, and these propagate by 

 the detachment of a vegetative cell, the new part becoming like the 

 parent. These plants are invested with flint, which is marked with 

 lines so minute that their true nature is still a subject of dispute. 

 Next to these come the Desmids, also minute, and, like the Dia- 

 toms, propagating by fission, but they are not invested with flint 

 and in some the first appearance of a generative process takes place 

 by what is termed conjugation ; that is, the junction of two indi- 

 viduals by a transverse tube, and the passage of the contents of 

 one to the other, a spore or seed being the result. 



Above these we rank the Confervacece, those green slimy masses 

 of threads we see in pools and on rocks ; these also reproduce by 

 conjugation, and the spore or seed is endowed with active motion 

 by means of cilia. Fucacece include the higher sea weeds, the 

 tangles and red weeds so common on our shores ; and now we 

 observe special male and female organs, antheridia containing sper- 

 matozoids, and archegonia containing a germ cell, which are en- 

 closed in a hollow receptacle. 



Next to these we place a small family — the Characece — found in 

 ditches and pools, remarkable for showing rotation of the colouring 

 matter inside the tubes of which they are composed. 



Above the Algas come Fungi, another great class, embracing 

 many thousand species, not only the mushrooms, toadstools, and 

 puffballs, but all the minute ones constituting mould, smut, and 

 rust, which attack decaying vegetables, and also occur in the tissues 

 of living plants. 



These also generate by antheridia and archegonia, and in their 

 minuter forms supply many elegant objects for the microscope. 



Next come the Lichens, those grey patches that coat over the 

 ruined tower, or storm- beat rock, or hang in shaggy tufts from aged 

 trees ; two forms of reproductive organs have been found, which 

 are collected in cups or shields, and some 3,000 species are known. 

 . All these groups are without a distinct axis of growth, and have 

 no leaves, and form a first great section — Thallogens. 



An easy step leads us to the Hepaticce, or Liverworts, moss-like 

 plants, with lobed leaves, and spiral threads mixed with the seeds ; 

 and from them again to the Mosses, which have simple leaves and 



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