MACFARLANE: SYNCHRONISM IN PLANT STRUCTURES 317 



The above are all shrubby or arborescent forms, and so are more 

 directly subject to changes of temperature than are species that 

 perennate by subterranean parts. The energizing factors are less 

 complex in the former; while in the latter, warmth, moisture, porosity 

 and chemical composition of the soil, become highly important govern- 

 ing factors. So the digestion and transfer of the reserve foods in 

 rhizomes, corms and bulbs is effected more gradually and the flowering 

 period is usually more prolonged, though the exactly synchronous 

 unfolding of the first blooms is as striking as in any of the shrubs 

 or trees. Of our three commonest spring flowers, Hepatica triloba, 

 Sanguinaria canadensis and Claytonia virginiana, the two first aver- 

 agely appear in bloom on April 9, and open successive flowers for a 

 period of 18 days in Hepatica, 10 to 12 days in Sanguinaria and about 

 25 days in Claytonia. Claytonia appears in bloom on April 12, aver- 

 agely. But in 19 13, our woods showed a sudden unfolding for the 

 first two on March 18 and of the last on March 20 or 21. 



Another herbaceous plant deserves special notice here as illustrating 

 an interesting phase in synchrony, namely, the dandelion. Like the 

 English daisy {Bellis perennis), this is a hardy plant which retains 

 wintergreen leaves and shelters amid close grassy sod. So very slight 

 changes of temperature in winter will cause both of these to unfold 

 their earliest flower-heads in apparently regular manner, specially if 

 growing in sheltered sunny places. But such by no means represents 

 the first exact growth period for the season, which for the dandelion 

 occurs averagely on April 23. Then, instead of the scant or occasional 

 heads of earlier date, our lawns show a sudden yellow coloring by 

 9 A.M. that is continued for almost a month thereafter, as successive 

 heads expand and as the florets in each successively open. During 

 1913, the behavior was noteworthy. For lawns were abundantly 

 yellowed over from January 16 to 20. But all suddenly closed and 

 were destroyed by frosts that succeeded from January 21 to March 2. 

 Then came a warm stimulating March, with the result that from the 

 15th of the month onward dandelions were abundant. 



In connection with his graduate class on the Gymnospermia, the 

 writer became interested from 1898 onward in the behavior of the 

 Japanese ginkgo tree {G. biloba), at first only with the aim of securing 

 appropriate material, but as the years passed the phenological relation 

 became of equal interest. Two large staminate trees grow near the 

 historic old Hamilton Mansion, adjoining the University Botanic 

 Garden. These suddenly and synchronously lengthened their catkins 

 in .1898 on the morning of May 2, and when visited on the succeeding 

 day few were still polleniferous. This suggested to the writer a 

 closer study of the subject from the standpoint of individual and species 



