1888.] NATURAL SCIENCES OF PHILADELPHIA. 277 



during winter, apparantly ready for the enormous draft on the stor- 

 age basins whicli the sudden burst of masses of young foliage must 

 entail in spring. All know how maples and (jther trees bleed on the 

 slightest wound before the bursting of the leaf, — and how completely 

 destitute of moisture the tissue seems a short time afterwards. All 

 bleeding ceases as the young leaf has fully expanded. Will not the 

 same necessity exist for a provision of moisture for the enormous 

 number of juicy succulent flowers the Yucca has suddenly to pro- 

 duce? May there not be enough and to spare in the earlier period, 

 with none to waste towards the last? These suggestions are all useful 

 as clews to further discoveries. The danger in science is that we 

 rest satisfied with plausibilities, and mistake them for facts. 



My object is to show that the much discussed Yucca is yet 

 a comparatively unexplored field; and that its unknown life- 

 history yet promises to be one of the most interesting subjects \ho 

 teleologist can possibly give his attention to. 



A dndy of the Hydranfiea in relation, to eros-'^-fertUization.- — That 

 many flowers are arranged for cross-fertilization needs no argu- 

 ment to sustain it, nor is it less certain that some floAvers can only 

 be fertilized through the aid of wind or insects. Spi-engel, it is well 

 known in the early part of the present century, placed this beyond 

 doubt. The great question is not. do plants generally cross-fertilize, 

 but why do they do it? ^Iv. Darwin's great work in this connection 

 h.as been to ])rove that plants abhor in and in breeding, that the 

 struggle for life is necessarily the chief object of existence, and that 

 cross-fertilization tends to make the race stronger and better fitted 

 to engage in this struggle than close breeding would do. The results 

 of many of Mr. Darwin's experiments sustain his views, as do those 

 of many others; but to my mind just as large a number do not 

 sustain them. Mr. Darwin himself has candidly .stated that con- 

 tinuous self fertilization does not in the least impair the fertility of 

 the race. Mere negative vigor is the leading advantage he finds 

 in crossed plants. (Cross and Self-fertilization, Chap. IX, p. 'P>2~.) 



It is not my object now to controvert the views of Mr. Darwin, or 

 or of his numerous followers. My view of one object of nature in 

 cross fertilization is to aid in production of variety. I have shown 

 ever since discussion grew warm on these subjects, that variation is 

 essential to the present order of thing?, — that nature, to be consistent 

 with herself, must provide for variations if for no other purpose than 

 to make variety. I now propose to show l)y some studies in 



