CORRESPONDENCE WITH DR. GRAY 



growth, that is, of size for another bud. In the little alga, 

 in my zoophyte chapter, sporules form only at a fixed 

 interval or distance from the extremity. In a branching 

 zoophyte, branches form at a fixed distance from the apex, 

 and at successive intervals, which intervals, cet.par., are 

 fixed in amount. It is the same in principle if the buds 

 form serrately at apex. There is something which deter- 

 mines these limits of distances; and, in the case of the 

 alga and others, it is good philosophy to say that the 

 process of growth at the apex will not allow (cet. par.) of 

 sporules forming within the specific distance. The 

 chemical forces required for growth at apex do not admit 

 of that different action of forces producing sporules within 

 the specific distance. The fact that size is a fundamental 

 element, as much as in a galvanic battery, and no doubt 

 for analogous reasons, is well shown in a brief article from 

 Van Beneden in the Journal just coming out. The 

 Campanularice, Ascidice, and other species that bud and 

 form compound groups, grow to some considerable size 

 by budding before ova are produced. The young animal 

 produces a succession of buds or polyps, and after the 

 dendroid group has reached a certain size, then it pro- 

 duces gemmules which give out a free young animal, of 

 peculiar shape (different from the polyps), and this young 

 animal produces ova. The ova again must go through 

 the same process. You observe the analogy to vegetation, 

 in which a series of buds usually forms and the plant thus 

 attains considerable size before a flower (an individual of 

 very different external form from the ordinary buds) is 

 produced, with the developing ovules. Steenstrup has 

 published a large work, which you have probably seen, 

 on Alternating Generations, all the facts of which 

 amount to nothing more, essentially, than what is com- 

 mon in vegetable life. Size, and size or length of inter- 

 val, must, therefore, be an important element in a [life] 

 of organic growth. This is the main point in my last 

 article. 



" Professor Henry, one evening at Washington, stated 

 to me that he considered the forces in animate nature 

 chemical forces ; but that there was a directrix (virtually) 

 behind all, modifying or governing the results. He com- 

 pared it to a steam-engine, whose forces within were 

 directed in their operation by the engineer. This is the 



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