8 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 30 Ser. 



approximately similar conditions of substratum and wave 

 action. Under other conditions the prostrate frond of N. 

 latissimum may become widely linear and irregularly lobed, 

 lose the toothed margin which forms one of the points of 

 resemblance to N. andersonianiim, and acquire a midrib and 

 nerves, in this case resembling the prostrate frond of N. 

 rufrechtiamim. Again, N. multilohum, which as a rule 

 selects sharply inclined or vertical rock-surfaces as a habi- 

 tat, forms by means of its prostrate frond orbicular patches 

 composed of the closely overlapping, broadly lobed, and 

 membranous portions of the creeping, prostrate frond. The 

 room afforded on the bare rock apparently favors the radial 

 development here exhibited; while the necessity for secur- 

 ing adequate thickness and firmness to meet the dash of the 

 waves has led to the close overlapping or dovetaihng of the 

 various divisions of the prostrate frond. 



It has already been remarked that the prostrate part of 

 the plant resembles in many respects the erect portion which 

 rises from it. This statement usually holds good with 

 regard to the shape and branching, but does not apply to 

 the venation. As a rule, a midrib or nerves are lacking 

 in the prostrate frond of those species whose erect fronds 

 are provided with such structures. 



Formation of Rhizoids. — A number of species also exhibit 

 a response apparently to the stimulus of contact, by send- 

 ing short processes or rhizoids from the surface of the 

 frond to the substratum to which they adhere. These pro- 

 cesses have been observed on the under surface of the 

 prostrate frond of N. rttfrechtianum, N. vtolacetim, N. 

 multilobimi, N. harveyaimm and JV. corallinarum, and are 

 recorded for several other species. Still more remarkable 

 is the instance observed of the formation of these rhizoids 

 in the case of a plant of N. violacctim. This specimen had 

 wrapped itself around portions of the thick frond of Prto- 

 nitis lanceolata, to whose surface numerous processes sent 

 forth from the surface of the Nitophylliim in contact with 

 the Prionitis had attached themselves. 



