290 HOEMEISTER, ON 



brane becomes by degrees a half solid gelatinous layer. 

 It is not until germination that this membrane becomes 

 smooth and firm on both sides. The expansion of the 

 cell-contents and of the innermost membrane which takes 

 place when the spore is sown upon moist ground, very 

 soon ruptures the outermost of the three membranes, and 

 shortly afterwards the middle one also, and both are stripped 

 off. The substance which is coloured red by caustic 

 potash remains attached to the inner wall of the innermost 

 membrane after the latter has become free, and even for 

 some time after its division into two cells. This substance 

 has the form of a layer composed of very minute particles, 

 and it may be detached by pressure from the cell-mem- 

 brane, 



Two facts in the process of development of the spores of 

 the Equisetaeege are of general interest. The spore-mem- 

 brane is here seen to increase in thickness after two differ- 

 ent modes of growth occurring side by side. There is 

 growth by apposition and growth by intussusception. To 

 the former is to be attributed the origin of the third and 

 fourth membranes, which are evidently produced from the 

 gradual hardening of layers of gelatinous matter spread 

 over the inner surface of the previously existing membranes. 

 To the latter belongs the centripetal growth of the elaters, 

 after their separation from one another, and the centrifugal 

 growth of the second and third membrane during and after 

 the formation of the fourth ; a growth which exhibits itself 

 in the granulation of the outer surfaces of both these mem- 

 branes. The second point, however, is the more important one, 

 viz., the remarkable modifications of the physical properties 

 and chemical reactions which each of the four membranes 

 of the spore undergoes during the process of development. 

 Each of them exhibits during a certain period of its exist- 

 ence the assumed characteristic relation between cellulose 

 and iodine and sulphuric acid ; but this relation is never 

 seen in the earliest states of development, nor is it constant. 

 The outer layer of the first membrane (i. e., the elaters), 

 and of the fourth membrane (even after the commencement 

 of germination), assume in the course of development the 

 character of a cuticle ; the second and third maintain that 



