THE HIGHER CRYPTOGAMIA. 309 



the exception of vessels, only of thin-walled prosenchymatal 

 cells, extends from the nearest vascular bundle of the root 

 for a short distance into the mass of cellular tissue. *This 

 structure, and also the position of the knob on the germ- 

 plant, correspond exactly with the structure and position of 

 the organ found on the embryo of the Polypodiaceae and 

 of other vascular cryptogams, which I have treated as the 

 continuously developing primary axis of the embryo with 

 the primordial tissue of the embryo, which bears on its lateral 

 surface the formative cells for further development.* 



In Botrychium this primary axis, if unusually developed \ 

 in thickness, may protrude laterally out of a fissure of the 

 prothalliuin. ,. The roots originate above the knob, the 

 oldest and longest of them being the nearest to it. The 

 direction of the roots is usually opposite to that of the 

 knob. The punctum vegetationis the growing end of the 

 secondary axis of the embryo- occupies the highest point 

 of the germ-plant (PI. XLT, fig. 10* ; PI. XLII, fig. l b ). 

 This bud, which consists of a flatly-conical group of thin- 

 walled cells, is situated at the base of a narrow, short, trans- 

 verse fissure in the blunt apex of the germ-plant, i. e., the 

 narrow opening of the vaginated scale-like first frond 

 of the latter (PI. XLII, fig. I 6 ). Germ-plants less deve- 

 loped than those above described were also found in quan- 

 tities (PL XLII, figs. 2, 3). They consisted only of the 

 globular knob, and the first or the first and an incipient 

 second root. The punctum vegetationis lay immediately 

 on the upper surface of the knob. In these plants no 

 trace of the prothallium could be perceived. They were 

 probably of the same age as those above mentioned, but 

 stunted and arrested in their development. 



The nature of the punctum vegetationis of the germ-plant 

 of Botrychium is a matter of special interest, inasmuch as it 

 must afford material assistance in deciding which of two 

 opposite opinions is the correct one. Roperf assumed that 

 the true stem rises vertically, but owing to the non-deve- 

 lopment of the internodes, imperceptibly ; that it produces 

 two leaves or fronds every year, whose stalks grow together 



* ' Griesebacli Jahresber., 5 1S52, p. 404. 



f 'Linusea,' vol. i, p. 460; 'Flora Mecklenbergs,' vol. i, p. 110. 



