M. Muller on the Development of the Lycopodiacese. 35 



3. The stem. The future situation of this is very evident in 

 the " germ " as a dark, circular expanded spot. This occurs near 

 the middle, and consists of cells filled with material for develop- 

 ment (PI. II. fig. 4«). This is the special point of vegetation 

 for stem and root, and the boundary of the germ. By the time 

 indeed that the stem has become so far visible that we can di- 

 stinguish clearly in the main axis, a terminal bud and an infe- 

 ferior, cylindrical, cellular portion (the stem itself), the vessels of 

 the stem and the terminal bud have already set out from that 

 spot. At a subsequent period the vessels of the root also origi- 

 nate at the same place ; so that this organ must be accounted part 

 of the main axis, notwithstanding that its originally erect and 

 independent development, apparently unconnected with that of 

 the bud of the stem, appears to indicate the contrary. 



The number of the vessels always amounts to two. This 

 number indeed occurs almost universally in Lycopod. denticula- 

 tum, since both the roots and the subsequently formed branches 

 divide dichotomously. At a later period, it is true, these two ves- 

 sels appear to become blended, but this union is only apparent, 

 and in the perfect stem the two orifices of the vessels are always 

 easily demonstrable in a transverse section. 



In their first stage they decidedly contain air, since when we 

 bring a stem at this period of its development under the micro- 

 scope, the vascular bundle appears all dark and filled with air- 

 bubbles (fig. 5 a). This arises probably from the circumstance, 

 that as the germinating plant lies in water, the latter penetrates 

 to a certain extent, accumulates in particular places among the 

 air contained in the vessels, and thus somewhat compresses it. 

 This is the more likely, since the vessel soon becomes so filled 

 with water, which could only be taken up through endosmose, 

 that the air is completely driven out, or perhaps in great part 

 mixed with the fluid. 



This stem now constitutes the whole of the as yet undivided, 

 main axis, and may thus be clearly distinguished from the branches 

 next produced. What the condition of this may be in the other 

 Lycopodia which do not belong to the genus Selaginella, I am 

 unable to say. It elongates only up to a certain limit, while the 

 terminal bud is becoming perfected at its apex. 



4. The terminal bud. When the stem is only just distinguish- 

 able, this organ is found upon it as a little head, of ovate form 

 and of a green colour. Within appear distinctly two, much 

 smaller, ovate bodies, situated opposite one another, which are 

 visible through the external, green envelope (fig. 1 d, fig. 2 «, a 

 lateral view), in which one body is in front of the other, and so 

 only one is visible. 



Examined more narrowly, the terminal bud is seen to consist 



3* 



