304 HOFMEISTER, ON 



course of their development a lateral, or downward direc- 

 tion, passing into the soil, and thus forming the first hori- 

 zontal subterranean rhizome of the Equisetum. The 

 sheathing leaves of this subterranean axis — which produces 

 a large quantity of adventitious roots — have also four teeth. 

 The shoots however which proceed from the bases of their 

 sheaths, of which some grow up to the light, and others 

 pierce vertically downwards to a great depth in the soil, are 

 considerably more vigorous than all the previous ones and 

 bear sheaths with five teeth. 



Adventitious buds are produced at the bases of the 

 upper sheathing leaves of the first shoots of the germ 

 plant. In Equisetum arvense one or two only and these 

 rarely and irregularly break through the bark of the 

 mother-shoot, and when developed form leafy branches of 

 very limited longitudinal growth. The limited number of 

 whorls (amounting on the first axis to barely three, and on 

 the succeeding axes to not more than four), forms a 

 striking contrast with the rich ramification of the vege- 

 tative shoots of old individuals. The formation of dwarf 

 shoots occurs only rarely and exceptionally on those 

 branches. 



The development of the germ-plant under favorable 

 circumstances is very rapid and vigorous. Germ-plants of 

 Equisetum arvense, produced from the prothallium in the 

 first week in June, formed by the beginning of August 

 seven generations of shoots, the last of them being then a 

 foot high, and lj'"m diameter, though bearing only four- 

 toothed sheaths. The strong side-shoots of subterranean 

 rhizomes became visible about the end of August. 



The reproduction of the Equisetacese from spores long 

 remained a mystery. Vaucher* in the spring of 1822 

 first brought forward the results of experimental sowing 

 of the spores, and he was followed by J. G. Agardh.f 

 They both saw only the first stages of development of 

 the prothallia, which Agardh described as cotyledons on 

 account of their two-lobed form. In the following year 

 Vaucher published some observations which gave a full 



* 'Mem. Soc. de Geneve, 3 i, (1817) p. 329. 

 f ' Mem. du Musee d'Histoire Nat.,' vol. ix. 



