28 THE PHENOMENON OF 



second generation, i.e. a sprout produced from the 

 thallus-like pro-embryo (prothallimi). The circumstances 

 are similar in Isoetes. Thus, even after very extensive 

 investigation, there probably does not remain to us one 

 single plant which, through the whole course of its deve- 

 lopment, from the germinal vesicle to the fruit, is but a 

 single, simple individual, uncomplicated by subordinate 

 propagation.* 



The subordinate condition of the propagation pre- 

 senting itself under the form of the production of sprouts 

 is expressed, secondly, in the fact that the particular 

 sprouts, and indeed the main sprout as well as the lateral 

 sprouts, do not, in the majority of cases, bring into exist- 

 ence all the stages of vegetable metamorphosis which 

 belong to the " stock " as a whole. Consequently there 

 exist, in reference to the share in the graduated structure 

 of the entire plant, sprouts of different kinds, and the 

 individual sprout on that account mostly represents only 

 more or less imperfectly the history of life of the plant. 



The deficiency of the sprout may relate either to its 

 commencement or its conclusion. The formation with 

 which a sprout commences mostly stands in relation to 

 the region of the parent-shoot from which it takes origin. 

 Thus we frequently see a series of sprouts, accurately 

 graduated in this respect, arise from successive regions of 

 the (absolute or relative) main-sprouts, e.g. sprouts 

 beginning with cataphyllary structures from the cataphyl- 

 lary region, with euphyllary leaves from the euphyllary 

 region, with hypsophyllary structures from the hypsophyl- 

 lary region. Hypericum perforatum and Mentha aquatica 

 are well-known examples exhibiting this phenomenon. 

 But a retrogression of the sprout to a lower formation, as 

 well as an advance to a higher, is possible. The former 



* See on this subject, Hofmeister, ' Erucht-bilding, &c. der holier. Krypto- 

 gamen," Leipsic, 1851. He however regards the fronds of ferns as branches, 

 a view which does not appear admissible. The first product from the pro- 

 thallum is the primary axis of a new individual, continued by a terminal 

 growth, but forking of the rhizome may occur, and this must depend on the 

 formation of secondary sprouts. In Isoetes the stem appears simple. A. H. 



