INTRODUCTION TO CRYPTOGAMTC BOTANY. 11 



inclosed in an integument which is itself composed of cells.* 

 Germination takes place by the extension of one or both 

 of the constituent membranes, in consequence of -which 

 they are essentially acotyledonous, and in general the point 

 of growth is indifferent, •]- though sometimes, as in certain 

 species of Uredo, Fuccinia, &c. (Fig. 6), indicated by spots 

 or apertures in the outer integument, through which the ger- 

 minating threads protrude exactly after the fashion of pollen 

 tubes. The spores, indeed, of such Fungi bear the closest 

 similarity in structure to many pollen grains, though their 

 functions are very different. 



These germinating tubes either reproduce the plant directly, 

 or give rise to a membranous expansion of a peculiar form, 

 or cushion-like swelling (prothallus), which, in due time, bears 

 the frond, fruit, or stem proper to the species.^ In the higher 

 Cryptogams, a single spore alone gives rise to a plant ; but even 

 amongst the foliaceous species, as in certain mosses, § a number 



* In Sdaginella a portion only is cellular in the form of a little disc. 

 The formation and thickening of this disc is all the germination which 

 takes place in the spores, which are, however, of very different value 

 from those of many other Cryptogams, as will be seen in the sequel. 



t There seems at first sight to be something like this in the fleshy 

 seeds of Crinum, and some other allied genera, as the radicle appears at 

 the point where the seed touches the soil ; but these bodies do not 

 consist of a mere mass of homogeneous cells, but contain, as will be seen 

 on close examination, a fact pointed out by Robert Brown in his Pro- 

 dromus, a distinct embryo, as perfectly formed as in other Amai-yllids. 



X It is quite clear that nothing ought to be reckoned as a cotyledon 

 which is not present in the perfect embryo. The cotyledons may be 

 soldered togetheras in Clintonia, much reduced as in endogens, or obso- 

 lete as in Cusouta, but still their presence may be regarded as almost 

 universal in the higher plants. It is, however, clear that they cannot 

 exist in Cryptogams where there is no embryo, and therefore perhaps 

 one of the most unobjectionable names which has been applied to them 

 is that of Acotyledons. The name of Pseudocotyledons or Cotyledonoids, 

 which has been given to the germinating threads, is founded on a false 

 notion as to the nature of their reproductive bodies, and should be 

 rejected as calculated to mislead. Some of the higher Cryptogams, 

 however, have an embryo, and in Sdaginella th e first two leaves a re 

 op posite, and have mucb jQifi-aPPearanc e of Cotyledons ! 



§, Kiitzing in Linnsea, vol. 8, tab. 7. 



